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Long-term maintenance of synaptic connections is important for brain function, which depends on varying proteostatic regulations to govern the functional integrity of neuronal proteomes. Proteostasis supports an interconnection of pathways that regulates the fate of proteins from synthesis to degradation. Defects in proteostatic signaling are associated with age-related functional decline and neurodegenerative diseases. Recent studies have advanced our knowledge of how cells have evolved distinct mechanisms to safely control protein homeostasis during synthesis, folding and degradation, and in different subcellular organelles and compartments. Neurodegeneration occurs when these protein quality controls are compromised by accumulated pathogenic proteins or aging to an irreversible state. Consequently, several therapeutic strategies, such as targeting the unfolded protein response and autophagy pathways, have been developed to reduce the burden of misfolded proteins and proved useful in animal models. Here, we present a brief overview of the molecular mechanisms involved in maintaining proteostatic networks, along with some examples linking dysregulated proteostasis to neuronal diseases.

Sorafenib is a multikinase inhibitor used for treatment of advanced hepatocellular carcinoma. Sorafenib resistance may be related to Src-induced cell migration and angiogenesis, which are regulated by cancer stem cell activation and release of vascular endothelial growth factor. Dasatinib is a Src inhibitor that inhibits Src phosphorylation and suppresses Src-associated cell migration and angiogenesis. This study investigated whether combined treatment with dasatinib can overcome sorafenib resistance. Hepatoma cell lines were used for sorafenib and/or dasatinib treatment. Cell viability, cell migration, molecular expressions, and release of vascular endothelial growth factor by hepatoma cells were evaluated. Hepatoma cell culture medium was applied on human umbilical vein endothelial cells to monitor angiogenesis promoted by the hepatoma cells. Sorafenib and dasatinib combined therapy suppressed cell viability of hepatoma cells synergistically. Dasatinib suppressed sorafenib-induced cell migration via inhibiting sorafenib-induced Src/FAK phosphorylation, cell-to-cell contact and cancer stem cell activation. Culture medium from Chang liver and PLC/PRF/5 cells suppressed angiogenesis of human umbilical vein endothelial cells with any treatment, whereas sorafenib-treated medium of HepG2 cells induced angiogenesis. This sorafenib-induced angiogenesis was then suppressed by dasatinib. Vascular endothelial growth factor released from hepatoma cells was also inhibited by combined treatment. Src/FAK phosphorylation and cancer stem cell activation inducing cell migration and angiogenesis may be the key factors of sorafenib resistance. Sorafenib and dasatinib combined treatment suppresses cell migration and angiogenesis by inhibiting the Src/FAK phosphorylation, cell-to-cell contact, cancer stem cell activation, and release of vascular endothelial growth factor.

Background An increasing number of studies support cancer stem cells as the reason for chemoresistance to sorafenib therapy in hepatocellular carcinoma (HCC), but the mechanism is still unclear. In this study, the mechanism of sorafenib resistance in cancer stem cells was examined by in vitro experiments and xenograft mouse model. Methods The expression of cancer stem cell markers in the Chang liver cell line and PLC/PRF/5 and HepG2 hepatoma cell lines were compared by immunoblot assay before and after sorafenib treatment in vitro. As a xenograft mouse model, subcutaneous injection of hepatoma cells followed by sorafenib therapy was performed in NU/NU mice. The effects of sorafenib therapy on tumor growth and cancer stem cell markers were studied. Angiogenesis associated with cancer stem cells was studied by immunoblot and immunohistochemistry assay. Results The expression of cancer stem cell markers was higher in PLC/PRF/5 and HepG2 cells than Chang liver cells, indicating that these hepatoma cells had more stemness-related characteristics. The cancer stem cell markers were upregulated in the hepatoma cell lines following sorafenib treatment in vitro. In the xenograft model, tumors from PLC/PRF/5 and HepG2 cells with high E-cadherin expression were more resistance to sorafenib therapy. However, the expression of cancer stem cell markers was not significantly different after sorafenib therapy in these tumors. Furthermore, we found that sorafenib therapy induced angiogenesis within tumors from high E-cadherin expressing hepatoma cells. Conclusion The mechanism of chemoresistance in sorafenib therapy in HCC may be the tumor angiogenesis associated with high E-cadherin expression in cancer stem cells.

Sorafenib is a multikinase inhibitor used for treatment of advanced hepatocellular carcinoma. Sorafenib resistance may be related to Src-induced cell migration and angiogenesis, which are regulated by cancer stem cell activation and release of vascular endothelial growth factor. Dasatinib is a Src inhibitor that inhibits Src phosphorylation and suppresses Src-associated cell migration and angiogenesis. This study investigated whether combined treatment with dasatinib can overcome sorafenib resistance.Hepatoma cell lines were used for sorafenib and/or dasatinib treatment. Cell viability, cell migration, molecular expressions, and release of vascular endothelial growth factor by hepatoma cells were evaluated. Hepatoma cell culture medium was applied on human umbilical vein endothelial cells to monitor angiogenesis promoted by the hepatoma cells.Sorafenib and dasatinib combined therapy suppressed cell viability of hepatoma cells synergistically. Dasatinib suppressed sorafenib-induced cell migration via inhibiting sorafenib-induced Src/FAK phosphorylation, cell-to-cell contact and cancer stem cell activation. Culture medium from Chang liver and PLC/PRF/5 cells suppressed angiogenesis of human umbilical vein endothelial cells with any treatment, whereas sorafenib-treated medium of HepG2 cells induced angiogenesis. This sorafenib-induced angiogenesis was then suppressed by dasatinib. Vascular endothelial growth factor released from hepatoma cells was also inhibited by combined treatment.Src/FAK phosphorylation and cancer stem cell activation inducing cell migration and angiogenesis may be the key factors of sorafenib resistance. Sorafenib and dasatinib combined treatment suppresses cell migration and angiogenesis by inhibiting the Src/FAK phosphorylation, cell-to-cell contact, cancer stem cell activation, and release of vascular endothelial growth factor.

Unstable cytokeratins are associated with tumor transformation in the development of human hepatocellular carcinoma. We previously demonstrated that the cytokeratin 18 was modulated and that a histone H3-specific modification occured, among members of the histone family, during the development of human hepatocellular carcinoma. Evidence suggested that the modification of histone H3 was highly correlated with the modulation of cytokeratin 18 and probably plays an important role in tumorigenesis of hepatocytes. Aberrant expression of histone deacetylase leading to imbalance between acetylation and deacetylation of histones may exhibit regulatory roles in tumor transformation. Recently we found that overexpression of histone deacetylase-1 and hypoacetylation of histone H3 were associated with hepatocellular carcinoma. The underlying roles of histone H3 modulation are discussed in this mini-review article.

Plectin involved in activation of kinases in cell signaling pathway and plays important role in cell morphology and migration. Plectin knockdown promotes cell migration by activating focal adhesion kinase and Rac1-GTPase activity in liver cells. Sorafenib is a multi-targeting tyrosine kinase inhibitor that improves patient survival on hepatocellular carcinoma. The aim of this study is to investigate the correlation between the expression of plectin and cell migration as well as the sensitivity of hepatoma cell lines exposing to sorafenib. Hepatoma cell lines PLC/PRF/5 and HepG2 were used to examine the level of plectin expression and cell migration in comparison with Chang liver cell line. In addition, sensitivity of the 3 cell lines to sorafenib treatment was also measured. Expression of plectin was lower in PLC/PRF/5 and HepG2 hepatoma cells than that of Chang liver cells whereas HepG2 and PLC/PRF/5 cells exhibit higher rate of cell migration in trans-well migration assay. Immunohistofluorecent staining on E-cadherin revealed the highest rate of collective cell migration in HepG2 cells and the lowest was found in Chang liver cells. Likewise, HepG2 cell line was most sensitive to sorafenib treatment and Chang liver cells exhibited the least sensitivity. The drug sensitivity to sorafenib treatment showed inverse correlation with the expression of plectin. We suggest that plectin deficiency and increased E-cadherin in hepatoma cells were associated with higher rates of cell motility, collective cell migration as well as higher drug sensitivity to sorafenib treatment.

Breast cancer treatment is multimodality. Prognosis prediction models depend on the tumor characteristics, neoplastic stage, intrinsic subtypes of oncogenes, molecular targets and dominant driving pathway. Immunohistochemical scores 4 (IHC4) is one of the most common and simplest prognostic models for breast cancer. IHC4 consists of four standard breast cancer biomarkers, including estrogen receptor (ER), progesterone receptor (PR), Ki-67 proliferative factor and human epidermal growth factor receptor 2 (Her-2/＂neu＂). The IHC4 scoring method was created mathematically and correlated with other genetic prediction models for breast cancer statistically. We have published Cdk5 and p35 proteins overexpression in some cancers including breast cancer. We inspected the expression of Cdk5 and p35 proteins to the IHC4 model in statistics. To date, several interesting proteins and genes are under investigation for linkage to the documented pathway in breast cancer. Even our results did not satisfy our expectation. We build a research model for the interesting proteins from bench to bed. In practice, the method is as simple as the purpose of the IHC4 method itself.

Synemin is a large intermediate filament protein that has been identified in all types of muscle cells. It plays a role in human muscle diseases; however, the role of synemin in tumor cell transformation has rarely been investigated. Because hepatocellular carcinoma cells are morphologically different from normal human hepatocytes, we hypothesized that altered synemin expression and cytoskeletal disorganization might underlie this pleomorphic transformation. To test this hypothesis, we studied synemin expression in hepatocellular carcinoma and liver tissues by immunohistochemistry and immunoblotting. In addition, we analyzed the expression level and organization of all cytoskeletal elements after synemin knock-down in human Chang liver cells. Previously we found that plectin knock-down in human Chang liver cells causes a reduction in cytokeratin 18 expression with effects on intermediate filament disorganization and altered cellular morphology. In this study we also compared the effects of synemin knock-down and plectin knock-down on the cytoskeleton expression and organization. The results revealed that synemin expression was down-regulated in human hepatocellular carcinoma compared with normal liver, which is similar to the plectin expression. Surprisingly, the expression of cytoskeletal elements (cytokeratin 18, actin and tubulin) was not influenced by synemin knock-down in human Chang liver cells. The organization of cytoskeletal networks was also unaltered after synemin knock-down. In conclusion, both plectin and synemin are down-regulated in human hepatocellular carcinoma in vivo and transformed human liver cell in vitro. However, the mechanism of cell transformation caused by synemin knock-down is different from that of plectin knock-down. Plectin, but not synemin, knock-down provoked liver cell transformation via suppressing cytokeratin 18 expression and disrupting intermediate filament networks. Synemin knock-down did not influence the cytoskeleton expression and organization of human Chang liver cells.

Aberrant histone deacetylase expression may cause imbalance between acetylation and deacetylation of histone and play roles in tumor transformation. We found that histone 3 was modulated in human hepatocellular carcinoma. We determined if histone 3 modulation is related to the aberrant expression of histone deacetylase.We analyzed human liver and hepatocellular carcinoma tissues and fibroblast and fibrosarcoma cell lines for the expression of histone 3, histone deacetylase 1 and acetylated histone 3 using immunohistochemistry, western blot and immunofluorescence.Histone deacetylase 1 and histone 3 were more strongly detected in hepatocellular carcinoma tissue and fibrosarcoma cells than in liver tissues and fibroblast cells, respectively. However, acetylated histone 3 was more strongly expressed in normal liver and fibroblast cells and less expressed in hepatocellular carcinoma and fibrosarcoma cells.Histone deacetylase 1 overexpression and hypoacetylation of histone 3 might play critical roles in the modulation of histone 3 in human hepatocellular carcinoma.

Background Plectin is one of the cytolinker proteins that play a crucial role in maintaining the integrity of cellular architecture. It is a component of desmosome complexes connecting cytoskeletal proteins and trans-membrane molecules. In epithelial cells, plectin connects cytokeratins and integrin α6β4 in hemidesmosomes anchoring to the extracellular matrix. In addition to the function of molecular adherent, plectin has been reported to exhibit functions affecting cellular signals and responsive activities mediated by stress, cellular migration, polarization as well as the dynamic movement of actin filaments. Plectin deficiency in hepatocellular carcinoma results in abnormal expression of cytokeratin 18 and disassembled hemidesmosome. Therefore, it is hypothesized that the plectin deficiency-mediated collapse of cytoskeleton may modulate cellular motility that is associated with consequent metastatic behaviors of cancer cells. Methods and results The cellular motility of plectin-deficient Chang liver cells generated by transient knockdown were analyzed by trans-well migration assay and the results revealed a higher migration rate. The confocal microscopy also demonstrated less organized and more polarized morphology as well as more focal adhesion kinase activity in comparison with that of the mock Chang liver cells. Furthermore, plectin-knockdown in Chang liver cells was associated with a higher activity of Rac1-GTPase in accordance with the results of the Rac1 pull-down assay. The immunohistochemical assay on human hepatocellular carcinoma showed that the expression of focal adhesion kinase was increased in the invasive front of tumor. Conclusion Plectin-deficient human hepatic cells exhibit higher cell motility associated with increase in focal adhesion kinase activity that are comparable to the properties of invasive hepatocellular carcinoma.

Intermediate filaments are important in building the architecture of liver cells and are proposed to interact with other cellular components. Among intermediate filament associated proteins, plectin is a versatile cytoskeletal linkage protein which has been shown to interact with a variety of cytoskeletal structures. Intermediate filament and plectin might play some roles in tumorigenesis of human hepatocellular carcinoma since cells of hepatocellular carcinoma were morphologically different from normal liver. Plectin exhibited wide distribution spectrum among various tissues, however, it was poorly investigated in human liver and hepatoma tissues. In this paper, we studied the plectin expression in 18 cases of human hepatocellular carcinoma and normal hepatocytes by immunohistochemistry. The results revealed that plectin expression was deficient in human hepatocellular carcinoma and was probably through post-translational modification. Many 0.4 to 0.8 microm-thick keratin bundles were found in intermediate filament extracts of liver and hepatoma tissues. These bundles were greater in diameter about 40 to 80 times of single intermediate filament. We speculated that intermediate filament organized into "filament bundles" to maintain the shape of normal cells. In cancer cells, plectin was deficient and the irregularly loosened filament bundles could cause pleomorphism of cancer cells.

Plectin is a versatile cytoplasmic cross-linking protein that connects intermediate filaments to microfilaments, microtubules, and membrane adhesion sites. The cross-linking functions of plectin help organize the cytoskeleton into a stable meshwork important for maintaining uniformity in cell size and shape. As cells of hepatocellular carcinoma are morphologically different from normal human hepatocytes, we hypothesized that altered plectin expression and cytoskeletal organization underlies this pleomorphic transformation. To test this hypothesis, we analyzed expression levels and organization of all cytoskeletal elements, including intermediate filaments, microfilaments, and microtubules, after plectin knockdown in human Chang liver cells. We found that expression of cytokeratin 18, but not actin or tubulin, was downregulated by suppression of plectin protein. Furthermore, cytokeratin networks were partially collapsed and actin-rich stress fibers were increased. The organization of microtubule networks, by contrast, was unaltered. These findings support our hypothesis that, via effects on cytoskeletal organization, plectin deficiency might play an important role in the transformation of human liver cells.

Plectin is a cross-linking protein that organizes the cytoskeleton into a stable meshwork that helps maintain the uniform size and shape of cells. As cells of hepatocellular carcinoma are morphologically different from healthy human hepatocytes, we hypothesized that plectin deficiency and cytoskeletal disorganization underlies this pleomorphic transformation. To test this hypothesis we induced apoptosis as the most accessible pathway for creating plectin deficiency status in vivo. We analyzed expression levels and organization of plectin and other cytoskeletal elements, including intermediate filaments, microfilaments, and microtubules, after staurosporine-induced apoptosis in human Chang liver cells. The results revealed the expression of plectin and cytokeratin 18 were downregulated in hepatocellular carcinoma tissues in vivo. The expression of actin and tubulin, however, were not altered. In vitro analysis indicated that plectin and cytokeratin 18 were cleaved following staurosporine-treatment of human Chang liver cells. Time course experiments revealed that plectin was cleaved 2h earlier than cytokeratin 18. The organization of plectin and cytokeratin 18 networks collapsed after staurosporine-treatment. Conclusively, degradation of plectin induced by staurosporine-treatment in liver cells resulted in cytoskeleton disruption and induced morphological changes in these cells by affecting the expression and organization of cytokeratin 18.

Hepatoma cells are morphologically different from those of the normal liver. Intermediate filaments (IFs) are important in building the cellular architecture and maintaining the outline of cells. Plectin is a cross-linking protein that organizes the cytoskeleton into a stable meshwork, which can maintain the uniform size and shape of hepatocytes. Apoptosis might be the most possible pathway for creating plectin deficiency in the in vivo state.Apoptosis was induced by staurosporine (STS) treatment in liver cells. The protein expression of cytokeratin 18 (CK18) and plectin as well as the morphology of the liver cells and the distribution of CK18 and plectin in the cells was studied after STS treatment.Plectin was cleaved in the liver cells during apoptosis and CK18 was modulated. Morphological changes were observed in the liver cells.By affecting the organization of IFs, plectin might play an important role in the pleomorphism of hepatoma cells and even the tumorigenesis of hepatoma.

Previously we found some low molecular weight proteins identified as histone in hepatocelluar carcinoma. Our objective was to clarify whether the coimmunoprecipitation of histone and cytokeratin 18 was an artifact or not.Histone 3 and cytokeratin 18 were investigated in three cases of human hepatocellular carcinoma and one case of normal liver tissue. Nuclei of the tissues were isolated; the proteins inside the nuclei were analyzed by Western blot.The results revealed histone was co-immunoprecipitated with cytokeratin 18 in hepatocellular carcinoma. It was speculated that modulation of the cytoskeleton in human hepatocellular carcinoma might disturb the organization of the nucleoskeleton. The unstable nucleoskeleton might further cause instability and fragility of nuclei, thus possibly exposing the histone and co-immunoprecipitating it with cytokeratin 18.The evidence might indicate that expression of histone 3 was highly related to modulation of cytokeratin 18 and might play an important role in tumorigenesis of hepatocellular carcinoma.

Tumor cells are morphologically different from normal cells. In this situation, we proposed that plectin, one of the intermediate filament associated proteins, might play some special roles in the tumorigenesis. Plectin exhibits a wide distribution spectrum among various tissues; however, it is scarcely investigated in tumor tissues including colorectal adenocarcinoma. In this study, we searched the plectin expression in 25 cases of colorectal adenocarcinoma and 10 cases of tubular adenoma with focal adenocarcinoma by immunohistochemical method. The results reveal that plectin is up-regulated in colorectal adenocarcinoma as well as in bizarre glands and locally invasive tumor nests in tubular adenoma, compared with normal colorectal mucosa. Over-expression of plectin in locally invasive tumor nests might help us in diagnosis of distinguish microinvasive foci from normal glands. The bizarre glands in adenoma might be precancerous lesions since the expression of plectin in them was identical to that of adenocarcinoma but in contrast to that of normal glands. The overexpression of plectin might affect the organization of cytoskeleton, which might further cause tumorigenesis and morphological change of colorectal epithelial cells.

Intermediate filaments are important in building the cellular architecture. Previously we found cytokeratin18 was modulated in human hepatocellular carcinoma. Plectin is a cross-linking protein that organizes the cytoskeleton into a stable meshwork, which can maintain the uniform size and shape of hepatocytes. Because the cells of hepatocellular carcinoma were morphologically different from the hepatocytes, we speculated that expression of plectin and organization of intermediate filament might play roles in the pleomorphism of hepatocellular carcinoma cells. In this paper, we studied the plectin expression of hepatocellular carcinoma and liver tissues by immunohistochemistry and immunoblot. The results revealed that plectin was deficient and cytokeratin18 was modulated in hepatocellular carcinoma. Furthermore, we knockdown the plectin mRNA in Chang cells, the result revealed the plectin was deficient and the organization of cytokeratin18 was altered. Conclusively, this study offers a hypothesis that plectin deficient might play an important role in the tumorigenesis of hepatocellular carcinoma.

Low-power laser irradiation (LPLI) has come into a wide range of use in medical field. Considering basic research, LPLI can enhance DNA synthesis and increases proliferation rate of human cells. But only a few data about the effects of LPLI on human liver or hepatoma cells are available. The cytoskeleton plays important roles in cell function and therefore is implicated in the pathogenesis of many human liver diseases, including malignant tumors. In our previous study, we found the stability of cytokeratin molecules in human hepatocytes was related to the intact microtubule network that was influenced by colchicine. In this study, we are going to search the effect of LPLI on proliferation of human hepatoma cell line HepG2 and J-5 cells. In addition, the stability of cytokeratin and synemin (one of the intermediate filament-associated proteins) were analyzed under the action of LPLI to evaluate the possible mechanism of LPLI effects on proliferation of human hepatoma cells. In experiment, HepG2 and J-5 cells were cultured in 24-well plate for 24 hours. After irradiation by 130 mW diode 808 nm GaAlAs continue wave laser in different time intervals, the cell numbers were counted. Western blot and immunofluorescent staining examined the expression and distribution of PCNA, cytokeratin and synemin. The cell number counting and PCNA expression were evaluated to determine the proliferation. The organization and expression of cytokeratin and synemin were studied to identify the stability of cytoskeleton affected by LPLI. The results revealed that proliferation of HepG2 and J-5 cells was inhibited by LPLI since the cell number and PCNA expression was reduced. Maximal effect was achieved with 90 and 120 seconds of exposure time (of energy density 5.85 J/cm2 and 7.8 J/cm2, respectively) for HepG2 and J-5, respectively. The decreased ratio of cell number by this dose of irradiation was 72% and 66% in HepG2 and J-5 cells, respectively. Besides that, the architecture of intermediate filaments in these cells was disorganized by laser irradiation. The expression of intermediate filament-associated protein, synemin, was also reduced. Two significant findings are raised in this study: (1) Diode 808 nm GaAlAs continuous wave laser has an inhibitory effect on the proliferation of human hepatoma cells line HepG2 and J-5. (2) The mechanism of inhibition might be due to down-regulation of synemin expression and alteration of cytokeratin organization that was caused by laser irradiation.

Low-power laser therapy has become popular in clinical applications including promoting wound healing and pain relief. However, effects of this photoradiation on human hepatoma cells are rarely studied. Previously, we found 808 nm gallium aluminum arsenide (GaAlAs) continuous wave laser had an inhibitory effect on the proliferation of human hepatoma cell lines HepG2 and J-5 at the energy density of 5.85 and 11.7 J/cm(2), respectively. The aim of the present study was to evaluate the possible mechanism of action of this photoradiation on HepG2 and J-5 cells. HepG2 and J-5 cells were cultured in 24-well plates for 24 h. After photoradiation by 130 mW 808 nm GaAlAs continuous wave laser for different time intervals (0, 30, 60, 90, 120, 150, and 180 s), Western blot and immunofluorescent staining were used to examine the expression and distribution of histone and cytoskeletal proteins. The cell counts as well as histone and synemin expression of HepG2 and J-5 cells were reduced by photoradiation at the energy density of 5.85 and 11.7 J/cm(2), respectively. Furthermore, the architecture of cytoskeletons and the distribution of intermediate filament-associated proteins (plectin and synemin) were disorganized by photoradiation. Photoradiation by 808 nm GaAlAs continuous wave laser at the energy density of 5.85 and 7.8 J/cm(2) inhibited the survival of human hepatoma cell lines. The mechanism might reduce synthesis of histone and synemin. Reduced histone synthesis might further reduce the proliferation rate of these cells. Reduced synemin synthesis might result in the destruction of the cytoskeleton. Therefore, the net effects by this photoradiation were reduced cell survival.

The stability of cytokeratin (CK) protein during tumor transformation in human hepatocellular carcinoma (HCC) was studied with molecular approach previously. The results demonstrated that the CK was modulated in human HCC. Besides this, three low molecular weight CK molecules (named HCC CK) were found. It indicated that these HCC CKs are undergone modulation from human hepatocyte CK18. However, there were many differences between the CK18 and HCC CK. First, the antigenecity of HCC CK had been changed since they could not be recognized by CAM5.2 antibody on Western blot. Second, the sequences of N-terminal residues of HCC CK were matched with those of the N-terminal residues of human histone. In this study, we confirmed that the HCC CK was actually to be histones because they reacted to anti-histone antibody on Western blot. Furthermore, we found that the histones of human HCC had been changed during the process of tumor transformation since they could be co-immunoprecipitated with CK18 and could be detected by Western blot while this phenomenon did not happen in the normal liver tissue. We also found that not all histones change in human HCC. Only H3 was detected on Western blot while H1, H2A, H2B, and H4 were not detected in human HCCs.

The cytoskeleton plays important roles in cell function and is therefore implicated in the pathogenesis of many human liver diseases, including malignant tumors. The stability of cytokeratin proteins during tumor transformation in human hepatocellular carcinoma has been studied with a molecular approach previously. The results demonstrate that the cytokeratin is modulated in human hepatocellular carcinoma. Besides this, three low molecular weight cytokeratin molecules (named HCC CK) are found.This indicates that these HCC CKs have undergone modulation from the human hepatocyte cytokeratin 18. We also checked the cytokeratin profile of the human hepatoma cell line PLC/PRF/5 with the same methods to ensure the HCC CK molecules are produced by modulation but not protein degradation. The stability of cytokeratin molecules was studied by a different approach. The cytokeratin compositions of human liver cells (Chang cell line) were analysed under the effects of microtubule-disrupting drug (colchicine) by SDS–PAGE, Western blot, immunoprecipitation using a commercially available monoclonal anti-cytokeratin 18 antibody and immunofluorescent staining. Within 1 h of treatment, the microtubule began to collapse and the filamentous structure was shortening. The microtubule had almost collapsed and became fragmented to form a lattice-like network after 24 h of treatment. The cytokeratin was modulated after long-term (24 h) treatment of colchicine, and the molecular weight became 14 kD and the antigenicity was lost. The stability of cytokeratin molecules was related to the intact microtubule network, after disruption of the microtubule the cytokeratin would be modulated. The intact microtubule network was a stabilizing factor of cytokeratin 18 in human liver cells.