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Background and Objective: Calmodulin-like protein CALML3 is an epithelial-specific protein regulated during keratinocyte differentiation in vitro. CALML3 expression is downregulated in breast cancers and transformed cell lines making it an attractive marker for tumor formation. The objective of this study was to survey CALML3 localization in normal epidermis and in hyperproliferative skin diseases including actinic keratosis, squamous and basal cell carcinoma as well as verruca and psoriasis and to compare CALML3 immunoreactivity with the proliferation marker Ki-67., Methods: Paraffin-embedded tissue sections from normal human skin and hyperproliferative skin disorders were examined by immunohistochemistry and analyzed for localization and expression of CALML3 and Ki-67., Results: CALML3 was strongly expressed in differentiating layers of normal skin, staining the periphery in suprabasal cells and exhibiting nuclear localization in the stratum granulosum. CALML3 nuclear localization was inversely correlated to Ki-67 staining in each disease, indicating that CALML3 nuclear presence is related to terminal cell differentiation and postmitotic state., Conclusions: Increased CALML3 expression in suprabasal layers is characteristic for differentiating keratinocytes in normal epidermis, and nuclear expression of CALML3 inversely correlates with expression of the proliferation marker Ki-67. This suggests that CALML3 is a useful marker for normal and benign hyperplastic epidermal development, whereas the loss of nuclear CALML3 indicates progression to a proliferative and potentially malignant phenotype.

Myo10 is an unconventional myosin with important functions in filopodial motility, cell migration, and cell adhesion. The neck region of Myo10 contains three IQ motifs that bind calmodulin (CaM) or the tissue-restricted calmodulin-like protein (CLP) as light chains. However, little is known about the mechanism of light chain binding to the IQ motifs in Myo10. Binding of CaM and CLP to each IQ motif was assessed by nondenaturing gel electrophoresis and by stopped-flow experiments using fluorescence-labeled CaM and CLP. Although the binding kinetics are different in each case, there are similarities in the mechanism of binding of CaM and CLP to IQ1 and IQ2: for both IQ motifs Ca(2+) increased the binding affinity, mainly by increasing the rate of the forward steps. The general kinetic mechanism comprises a two-step process, which in some cases may involve the binding of a second IQ motif with lower affinity. For IQ3, however, the kinetics of CaM binding is very different from that of CLP. In both cases, binding in the absence of Ca(2+) is poor, and addition of Ca(2+) decreases the K(d) to below 10 nM. However, while the CaM binding kinetics are complex and best fitted by a multistep model, binding of CLP is fitted by a relatively simple two-step model. The results show that, in keeping with growing structural evidence, complexes between CaM or CaM-like myosin light chains and IQ motifs are highly diverse and depend on the specific sequence of the particular IQ motif as well as the light chain.

Epidermal wound healing is required for normal skin barrier function. Cell motility is a key factor in the ability of keratinocytes to heal epithelial damage. Calmodulin-like protein (CLP) is an epithelial-specific Ca(2+)-binding protein that is regulated during terminal keratinocyte differentiation. CLP is a specific light chain of unconventional myosin-10 (Myo10) and its expression increases filopodial length, filopodial number, and Myo10-dependent cell motility in vitro. However, the effects of CLP expression on keratinocyte motility are unknown. Here we used cultured human keratinocytes to study the role of CLP in regulating Myo10 and the effects of Myo10 and CLP on cell migration. CLP and Myo10 expression were correlated in vitro and required for keratinocyte motility in wound-healing assays. We examined the localization of CLP in wounded skin by immunohistochemistry and found an upregulation and peripheral localization of CLP in the basal and suprabasal cells adjacent to and immediately over the wound bed in vivo. The results suggest that increased CLP expression and CLP-mediated Myo10 function are important for skin differentiation and wound reepithelialization.

Purpose: The purpose of this study was to test whether calmodulin-like protein (CLP) is expressed in normal human oral mucosal cells and if downregulation of CLP occurs in malignant transformation., Materials and Methods: Oral mucosal tissue was taken from three individuals in a double-blind manner. The samples were cut, measured, and homogenized. Total RNA was extracted and reverse transcribed. Each cDNA sample was subjected to polymerase chain reaction (PCR). PCR fragments were purified, cloned, and sequenced to verify the presence of CLP. Three oral mucosal tissue samples with biopsy-confirmed squamous cell carcinoma were obtained. These samples demonstrated regions of normal epithelial cells as well as invasive squamous cell carcinoma. One normal breast epithelial sample was also obtained for positive control. Sections were stained with an affinity-purified CLP antibody and counterstained with a diluted hematoxylin. Two observers evaluated the specimens for expression of CLP. Staining patterns and intensity were noted in normal oral mucosa, comparing them to the normal breast epithelium sample. Staining patterns and intensity were then observed in squamous tumor cells, comparing them to the patterns of benign squamous mucosa., Results: CLP coding sequences were positively identified from the normal oral mucosal tissue samples by reverse transcription and polymerase chain reaction (RT-PCR) with 100% identity to the published CLP sequence (accession #M58026). In the three oral mucosa tissue samples with known squamous cell carcinoma, expression of CLP was readily detected in areas of normal oral mucosa, while a notable downregulation of CLP expression occurred in areas of malignant transformation. The staining intensity was equivalent to the staining seen in the benign breast epithelium used as a control. In the areas of squamous cell carcinoma, a decrease in CLP immunoreactivity occurred. There was a sharp contrast in staining quality and clarity between benign and malignant tissue. In the majority of the carcinoma regions, a complete lack of immunoreactivity was noted., Conclusions: The RNA for human CLP is found in normal oral mucosa. CLP expression is seen in normal oral mucosa with a downregulation of CLP expression in malignant transformation.

Calmodulin-like protein (CLP) is a specific light chain of unconventional myosin-10 (Myo10) and enhances Myo10-dependent filopodial extension. Here we show that phenylalanine-795 in the third IQ domain (IQ3) of Myo10 is critical for CLP binding. Remarkably, mutation of F795 to alanine had little effect on calmodulin binding to IQ3. Fluorescence microscopy and time-lapse video microscopy showed that HeLa cells expressing CLP and transiently transfected with GFP-Myo10-F795A exhibited significantly shorter filopodia and decreased intrafilopodial motility compared to wildtype GFP-Myo10-transfected cells. Thus, F795 represents a unique anchor for CLP and is essential for CLP-mediated Myo10 function in filopodial extension and motility.

Myosin-10 (Myo10) is involved in processes ranging from filopodial formation and extension to spindle orientation during cell division. Myo10 contains three IQ motifs that bind calmodulin and calmodulin-like protein (CLP) as light chains. We recently found that CLP expression up-regulates Myo10, leading to increased Myo10-dependent cell motility and filopodial extension [R.D. Bennett, et al., J. Biol. Chem. 282 (2007) 3205-3212]. CLP-dependent Myo10 up-regulation occurs without increase in Myo10 mRNA. We followed Myo10 degradation in vivo and in vitro and found that it was unaffected by CLP. Myo10 decayed rapidly with a half-life of approximately 2.5h. Using an in vitro transcription/translation system we determined that CLP increased Myo10 translation, resulting in a higher relative accumulation of Myo10 in the presence than in the absence of CLP. Our data suggest that CLP functions to increase translation of Myo10 possibly by acting as a chaperone for the emerging Myo10 heavy chain protein.

Human calmodulin-like protein (CLP) is an epithelial-specific protein that is expressed during cell differentiation but down-regulated in primary cancers and transformed cell lines. Using stably transfected and inducible HeLa cell lines, we found that CLP expression did not alter the proliferation rate and colony-forming potential of these cells. However, remarkable phenotypic changes were observed in CLP-expressing compared with control cells. Soft agar colonies of CLP-expressing cells had rough boundaries, with peripheral cells migrating away from the colony. Cells expressing CLP displayed a striking increase in the number and length of myosin-10-positive filopodia and showed increased mobility in a wound healing assay. This increase in wound healing capacity was prevented by small interference RNA-mediated down-regulation of myosin-10. Fluorescence microscopy and Western blotting revealed that CLP expression results in up-regulation of its target protein, myosin-10. This up-regulation occurs at the protein level by stabilization of myosin-10. Thus, CLP functions by increasing the stability of myosin-10, leading to enhanced myosin-10 function and a subsequent increase in filopodial dynamics and cell migration. In stratified epithelia, CLP may be required during terminal differentiation to increase myosin-10 function as cells migrate toward the upper layers and establish new adhesive contacts.