Novel role for the testis-enriched HSPA2 protein in regulating epidermal keratinocyte differentiation.

HSPA2, a poorly characterized member of the HSPA (HSP70) chaperone family, is a testis-enriched protein involved in male germ cell differentiation. Previously, we revealed that HSPA2 is present in human stratified epithelia, including epidermis, however the contribution of this protein to epithelial biology remained unknown. Here, we show for the first time that HSPA2 is expressed in basal epidermal keratinocytes, albeit not in keratinocytes exhibiting features attributed to primitive undifferentiated progenitors, and participates in the keratinocyte differentiation process. We found that HSPA2 is dispensable for protection of HaCaT keratinocytes against heat shock-induced cytotoxicity. We also shown that lentiviral-mediated shRNA silencing of HSPA2 expression in HaCaT cells caused a set of phenotypic changes characteristic for keratinocytes committed to terminal differentiation such as reduced clonogenic potential, impaired adhesiveness and increased basal and confluency-induced expression of differentiation markers. Moreover, the fraction of undifferentiated cells that rapidly adhered to collagen IV was less numerous in HSPA2-deficient cells than in the control. In a 3D reconstructed human epidermis model, HSPA2 deficiency resulted in accelerated development of a filaggrin-positive layer. Collectively, our results clearly show a link between HSPA2 expression and maintenance of keratinocytes in an undifferentiated state in the basal layer of the epidermis. It seems that HSPA2 could retain keratinocytes from premature entry into the terminal differentiation process. Overall, HSPA2 appears to be necessary for controlling development of properly stratified epidermis and thus for maintenance of skin homeostasis.

Bis-anthracycline WP760 abrogates melanoma cell growth by transcription inhibition, p53 activation and IGF1R downregulation.

Anthracycline chemotherapeutics, e.g. doxorubicin and daunorubicin, are active against a broad spectrum of cancers. Their cytotoxicity is mainly attributed to DNA intercalation, interference with topoisomerase activity, and induction of double-stranded DNA breaks. Since modification of anthracyclines can profoundly affect their pharmacological properties we attempted to elucidate the mechanism of action, and identify possible molecular targets, of bis-anthracycline WP760 which previously demonstrated anti-melanoma activity at low nanomolar concentrations. We studied the effect of WP760 on several human melanoma cell lines derived from tumors in various development stages and having different genetic backgrounds. WP760 inhibited cell proliferation (IC50 = 1-99 nM), impaired clonogenic cell survival (100 nM), and inhibited spheroid growth (≥300 nM). WP760 did not induce double-stranded DNA breaks but strongly inhibited global transcription. Moreover, WP760 caused nucleolar stress and led to activation of the p53 pathway. PCR array analysis showed that WP760 suppressed transcription of ten genes (ABCC1, MTOR, IGF1R, EGFR, GRB2, PRKCA, PRKCE, HDAC4, TXNRD1, AKT1) associated with, inter alia, cytoprotective mechanisms initiated in cancer cells during chemotherapy. Furthermore, WP760 downregulated IGF1R and upregulated PLK2 expression in most of the tested melanoma cell lines. These results suggest that WP760 exerts anti-melanoma activity by targeting global transcription and activation of the p53 pathway and could become suitable as an effective therapeutic agent.

Cell type-dependent modulation of the gene encoding heat shock protein HSPA2 by hypoxia-inducible factor HIF-1: Down-regulation in keratinocytes and up-regulation in HeLa cells.

HSPA2 belongs to the multigene HSPA family, whose members encode chaperone proteins. Although expression and function of HSPA2 is mainly associated with spermatogenesis, recent studies demonstrated that in humans, the gene is active in various cancers, as well as in normal tissues, albeit in a cell type-specific manner. In the epidermis, HSPA2 is expressed in keratinocytes in the basal layer. Currently, the mechanisms underlying the regulation of HSPA2 expression remain unknown. This study was aimed at determining whether HIF-1 and its binding site, the hypoxia-response element (HRE) located in the HSPA2 promoter, are involved in HSPA2 regulation. As a model system, we used an immortal human keratinocyte line (HaCaT) and cervical cancer cells (HeLa) grown under control or hypoxic conditions. Using an in vitro gene reporter assay, we demonstrated that in keratinocytes HSPA2 promoter activity is reduced under conditions that facilitate stabilization of HIF-1α, whereas HIF-1 inhibitors abrogated the suppressive effect of hypoxia on promoter activity. Chromatin immunoprecipitation revealed that HIF-1α binds to the HSPA2 promoter. In keratinocytes, hypoxia or overexpression of a stable form of HIF-1α attenuated the expression of endogenous HSPA2, whereas targeted repression of HIF-1α by RNAi increased transcription of HSPA2 under hypoxia. Conversely, in HeLa cells, HSPA2 expression increased under conditions that stimulated HIF-1α activity, whereas inhibition of HIF-1α abrogated hypoxia-induced up-regulation of HSPA2 expression. Taken together, our results demonstrate that HIF-1 can exert differential, cell context-dependent regulatory control of the HSPA2 gene. Additionally, we also showed that HSPA2 expression can be stimulated during hypoxia/reoxygenation stress.

Global gene expression profiling in three tumor cell lines subjected to experimental cycling and chronic hypoxia.

Hypoxia is one of the most important features of the tumor microenvironment, exerting an adverse effect on tumor aggressiveness and patient prognosis. Two types of hypoxia may occur within the tumor mass, chronic (prolonged) and cycling (transient, intermittent) hypoxia. Cycling hypoxia has been shown to induce aggressive tumor cell phenotype and radioresistance more significantly than chronic hypoxia, though little is known about the molecular mechanisms underlying this phenomenon. The aim of this study was to delineate the molecular response to both types of hypoxia induced experimentally in tumor cells, with a focus on cycling hypoxia. We analyzed in vitro gene expression profile in three human cancer cell lines (melanoma, ovarian cancer, and prostate cancer) exposed to experimental chronic or transient hypoxia conditions. As expected, the cell-type specific variability in response to hypoxia was significant. However, the expression of 240 probe sets was altered in all 3 cell lines. We found that gene expression profiles induced by both types of hypoxia were qualitatively similar and strongly depend on the cell type. Cycling hypoxia altered the expression of fewer genes than chronic hypoxia (6,132 vs. 8,635 probe sets, FDR adjusted p<0.05), and with lower fold changes. However, the expression of some of these genes was significantly more affected by cycling hypoxia than by prolonged hypoxia, such as IL8, PLAU, and epidermal growth factor (EGF) pathway-related genes (AREG, HBEGF, and EPHA2). These transcripts were, in most cases, validated by quantitative reverse transcription polymerase chain reaction (qRT-PCR). Our results indicate that experimental cycling hypoxia exerts similar, although less intense effects, on the examined cancer cell lines than its chronic counterpart. Nonetheless, we identified genes and molecular pathways that seem to be preferentially regulated by cyclic hypoxia.

HSPA2 is expressed in human tumors and correlates with clinical features in non-small cell lung carcinoma patients.

BACKGROUND/AIM: It has been shown that HSPA2 protein, a testis-enriched member of HSPA/HSP70 family, is important for cancer cell growth and metastasis. However, the status of HSPA2 expression in tumors and its clinical/prognostic significance are obscure. Herein we aimed to investigate the expression of HSPA2 in various types of tumors and to determine the possible clinical and prognostic significance of HSPA2 in non-small cell lung carcinoma (NSCLC). MATERIALS AND METHODS: Tissue microarrays and postoperative NSCLC tumors were tested for HSPA2 by immunohistochemistry. RESULTS: HSPA2 is expressed in the majority of tumor histotypes. In NSCLC patients (n=85), nuclear HSPA2 expression was associated with histology, TNM staging and prognosis. High HSPA2 expression was significantly related to shorter overall survival (OS) in stage I-II patients. In multivariate analysis, high HSPA2, together with stage IIIA and male sex, were associated with shorter OS in the whole group. CONCLUSIONS: As exemplified in NSCLC the status of HSPA2 in human tumors may have certain prognostic significance.

Melanoma-associated genes, MXI1, FN1, and NME1, are hypoxia responsive in murine and human melanoma cells.

Hypoxia can influence aggressiveness of melanoma by inducing specific gene expression profiles. In our previous microarray study, we identified more than 430 hypoxia-responsive genes in the B16-F10 murine melanoma cell line in vitro. Of the genes identified, seven genes: galectin 3 (Lgals3), melanoma cell adhesion molecule (Mcam), fibronectin 1 (Fn1), signal transducer and activator of transcription 3 (Stat3), microphthalmia-associated transcription factor (Mitf), max interacting protein 1 (Max1), and non-metastatic cells 1, protein (NM23A) expressed in (Nme1) are known to be associated with melanoma, but have not yet been reported as being regulated by hypoxia in human melanoma cells. In this study, we investigated whether the expression of these genes is modulated by hypoxia in microdissected areas of experimental B16-F10 tumors in vivo, as well as in commercially available human melanoma cell lines (WM35, WM1552C, WM793B, WM278, 1205Lu, and 451Lu) exposed to hypoxic conditions in vitro. Our analysis revealed significant agreement between the in-vitro and in-vivo results showing that all genes except Mitf were hypoxia regulated in the oxygen-deprived tumor regions (P<0.05). In contrast, three genes (NME1, MXI1 and FN1) proved to be hypoxia regulated in both human and mouse melanoma cells (P<0.05). Our results link these genes, for the first time, with hypoxic microenvironment of melanoma and imply that the widely used B16-F10 melanoma experimental tumor model could be a convenient research tool for further investigation of their role in the development and course of this malignancy.