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There are limited therapeutic options for patients with advanced prostate cancer (PCa). We previously found that heat shock factor 1 (HSF1) expression is increased in PCa and is an actionable target. In this manuscript, we identify that HSF1 regulates the conversion of homocysteine to cystathionine in the transsulfuration pathway by altering levels of cystathionine-β-synthase (CBS). We find that HSF1 directly binds the CBS gene and upregulates CBS mRNA levels. Targeting CBS decreases PCa growth and induces tumor cell death while benign prostate cells are largely unaffected. Combined inhibition of HSF1 and CBS results in more pronounced inhibition of PCa cell proliferation and reduction of transsulfuration pathway metabolites. Combination of HSF1 and CBS knockout decreases tumor size for a small cell PCa xenograft mouse model. Our study thus provides new insights into the molecular mechanism of HSF1 function and an effective therapeutic strategy against advanced PCa. HSF1 regulates the conversion of homocysteine to cystathionine in the trans-sulfuration pathway by altering levels of cystathionine-β-synthase (CBS), and targeting CBS decreases pancreatic cancer growth while leaving benign prostate cells largely unaffected. [ABSTRACT FROM AUTHOR]

Simple Summary: Breast cancer is the second leading cause of cancer-related death in women. The increase in effective therapies and breast cancer survivorship has highlighted the cardiotoxic effects of many chemotherapies. In this study, we investigated Serine-Threonine Kinase 3 (STK3), a kinase in the Hippo Tumor-Suppressor Pathway, as a potential drug target to both inhibit breast cancer growth and mitigate chemotherapy-induced cardiotoxic damage. According to its canonical role, STK3 acts as a tumor suppressor, but STK3 is amplified and correlates with worse outcomes for breast cancer patients, suggesting that it plays a distinct role in breast cancer. Using genetic and pharmacological experiments in breast cancer and cardiomyocyte cell lines, we show that STK3 inhibition simultaneously slows breast cancer growth and invasion while providing protection to cardiomyocytes from doxorubicin-induced cardiotoxicity. Breast cancer (BCa) is the most prevalent type of cancer in women. Several therapies used in the treatment of breast cancer are associated with clinically important rates of cardiovascular toxicity during or after treatment exposure, including anthracyclines. There is a need for new BCa therapeutics and treatments that mitigate chemotherapy-induced cardiotoxicity in BCa. In this study, we examine the effects of Serine/Threonine Kinase 3 (STK3) inhibition in the context of BCa therapy and cardioprotection from doxorubicin. STK3 (also known as MST2) is a key member of the Hippo Tumor-Suppressor Pathway, which regulates cell growth and proliferation by inhibiting YAP/TAZ co-transcription factors. Canonically, STK3 should restrict BCa growth; however, we observed that STK3 is amplified in BCa and associated with worse patient outcomes, suggesting a noncanonical pro-tumorigenic role. We found BCa cell lines have varying dependence on STK3. SUM52PE cells had the highest expression and dependence on STK3 in genetic and pharmacological assays. MCF-7 and MDA-MB-231 were less sensitive to STK3 targeting in standard proliferation assays, but were STK3 dependent in colony formation and matrigel invasion assays. In contrast, STK3 inhibition mitigated the toxic effects of doxorubicin in H9C2 rat cardiomyocytes by increasing YAP expression. Importantly, STK3 inhibition in BCa cells did not interfere with the therapeutic effects of doxorubicin. Our studies highlight STK3 is a potential molecular target for BCa with dual therapeutic effects: suppression of BCa growth and progression, and chemoprotection in cardiomyocytes. [ABSTRACT FROM AUTHOR]

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Hair follicles regenerate periodically by spontaneously undergoing cycles of growth, regression, and relative quiescence. During the hair cycle, follicle stem cells residing in a specialized niche remain quiescent, and they are stimulated to proliferate throughout the growth phase of the hair follicle. Although cell cycle regulators play a prominent role during the activation of hair follicle stem cells, the identity and the role of these regulators have not been confirmed. Herein, we reported that stem cells located in the bulge region of the HF (BuSCs) express high levels of cyclin‐dependent kinase 4 (CDK4) through the quiescent phase of the hair cycle. Using gain‐ and loss‐of‐function studies, we have determined that the CDK4 protein level affects the number of BuSCs. Transgenic expression of CDK4 in the bulge region of the hair follicles reduces the number of BuSCs, whereas CDK4 ablation resulted in an increasing number of BuSCs. These results suggest that deregulation of CDK4 protein levels contributes to distorting the self‐renewal/proliferation balance and, in turn, altering the number of BuSCs. [ABSTRACT FROM AUTHOR]

The renin-angiotensin system, through its type 1 and type 2 angiotensin receptors (AT1R and AT2R, respectively) may have a role in prostate cancer. The objective of this pilot study was to explore that potential role by determining whether the AT1R blocker, losartan, would reduce the growth of LAPC-4 prostate cancer xenografts in nude mice. We also evaluated the tumor growth effects of using angiotensin II to activate both AT1R and AT2R simultaneously. Our data showed that losartan decreased tumor volumes by 56% versus control. This decrease reached statistical significance at day 54 (p = 0.0014). By day 54, Ki67 was also reduced in the losartan group, though not significantly so (p = 0.077). Losartan had no significant effect on AT1R or AT2R expression. Despite significant increases in both AT1R and AT2R at day 29 (p = 0.043 and 0.038, respectively), the administration of angiotensin II did not result in any significant differences in tumor volumes or ki67 at any time point. These data suggest that selective activation and induction of AT2R coupled with blockade of AT1R may slow prostate cancer growth. Future larger studies are needed to confirm these results. [ABSTRACT FROM AUTHOR]

Signal transducer and activator of transcription 3 (Stat3) is a cytoplasmic protein that is activated in response to cytokines and growth factors and acts as a transcription factor. Stat3 plays critical roles in various biological activities including cell proliferation, migration, and survival. Studies using keratinocyte-specific Stat3-deficient mice have revealed that Stat3 plays an important role in skin homeostasis including keratinocyte migration, wound healing, and hair follicle growth. Use of both constitutive and inducible keratinocyte-specific Stat3-deficient mouse models has demonstrated that Stat3 is required for both the initiation and promotion stages of multistage skin carcinogenesis. Further studies using a transgenic mouse model with a gain of function mutant of Stat3 (Stat3C) expressed in the basal layer of the epidermis revealed a novel role for Stat3 in skin tumor progression. Studies using similar Stat3-deficient and gain-of-function mouse models have indicated its similar roles in ultraviolet B (UVB) radiation-mediated skin carcinogenesis. This paper summarizes the use of these various mouse models for studying the role and underlying mechanisms for the function of Stat3 in skin carcinogenesis. Given its significant role throughout the skin carcinogenesis process, Stat3 is an attractive target for skin cancer prevention and treatment. [ABSTRACT FROM AUTHOR]

Loss of the cyclin-dependent kinase inhibitor p27Kip1 leads to an overall increase in animal growth, pituitary tumors, and hyperplasia of hematopoietic organs, yet it is unknown whether all cells function autonomously in response to p27Kip1 activity or whether certain cells take cues from their neighbors. In addition, there is currently no genetic evidence that tumor suppression by p27Kip1 is cell-autonomous because biallelic gene inactivation is absent from tumors arising in p27Kip1 hemizygous mice. We have addressed these questions with tissue-specific targeted mouse mutants and radiation chimeras. Our results indicate that the suppression of pars intermedia pituitary tumors by p27Kip1 is cell-autonomous and does not contribute to overgrowth or infertility phenotypes. In contrast, suppression of spleen growth and hematopoietic progenitor expansion is a consequence of p27Kip1 function external to the hematopoietic compartment. Likewise, p27Kip1 suppresses thymocyte hyperplasia through a cell-nonautonomous mechanism. The interaction of p27Kip1 loss with epithelial cell-specific cyclin-dependent kinase 4 overexpression identifies the thymic epithelium as a relevant site of p27Kip1 activity for the regulation of thymus growth. [ABSTRACT FROM AUTHOR]

The proto-oncogene c-myc encodes a transcription factor that is implicated in the regulation of cellular proliferation, differentiation, and apoptosis and that has also been found to be deregulated in several forms of human and experimental tumors. We have shown that forced expression of c-myc in epithelial tissues of transgenic mice (K5-Myc) resulted in keratinocyte hyperproliferation and the development of spontaneous tumors in the skin and oral cavity. Although a number of genes involved in cancer development are regulated by c-myc, the actual mechanisms leading to Myc-induced neoplasia are not known. Among the genes regulated by Myc is the cyclin-dependent kinase 4 (CDK4) gene. Interestingly, previous studies from our laboratory showed that the overexpression of CDK4 led to keratinocyte hyperproliferation, although no spontaneous tumor development was observed. Thus, we tested the hypothesis that CDK4 may be one of the critical downstream genes involved in Myc carcinogenesis. Our results showed that CDK4 inhibition in K5-Myc transgenic mice resulted in the complete inhibition of tumor development, suggesting that CDK4 is a critical mediator of tumor formation induced by deregulated Myc. Furthermore, a lack of CDK4 expression resulted in marked decreases in epidermal thickness and keratinocyte proliferation compared to the results obtained for K5-Myc littermates. Biochemical analysis of the K5-Myc epidermis showed that CDK4 mediates the proliferative activities of Myc by sequestering p21Cip1 and p27Kip1 and thereby indirectly activating CDK2 kinase activity. These results show that CDK4 mediates the proliferative and oncogenic activities of Myc in vivo through a mechanism that involves the sequestration of specific CDK inhibitors. [ABSTRACT FROM AUTHOR]

In a previous study, we reported that overexpression of cyclin-dependent kinase-4 (CDK4) in mouse epidermis results in epidermal hyperplasia, hypertrophy and severe dermal fibrosis. In this study, we have investigated the susceptibility to skin tumor formation by forced expression of CDK4. Skin tumors from transgenic mice showed a dramatic increase in the rate of malignant progression to squamous cell carcinomas (SCC) in an initiation-promotion protocol. Histopathological analysis of papillomas from transgenic mice showed an elevated number of premalignant lesions characterized by dysplasia and marked atypia. Interestingly, transgenic mice also developed tumors in initiated but not promoted skin, demonstrating that CDK4 replaced the action of tumor promoters. These results suggest that expression of cyclin D1 upon ras activation synergizes with CDK4 overexpression. However, cyclin D1 transgenic mice and double transgenic mice for cyclin D1 and CDK4 did not show increased malignant progression in comparison to CDK4 transgenic mice. Biochemical analysis of tumors showed that CDK4 sequesters the CDK2 inhibitors p27Kip1 and p21Cip1, suggesting that indirect activation of CDK2 plays an important role in tumor development. These results indicate that, contrary to the general assumption, the catalytic subunit, CDK4, has higher oncogenic activity than cyclin D1, revealing a potential use of CDK4 as therapeutic target.Oncogene (2004) 23, 1863-1873. doi:10.1038/sj.onc.1207309 Published online 1 December 2003 [ABSTRACT FROM AUTHOR]