Our long-term goal is to investigate the therapeutic potential and the underlying molecular mechanisms of maspin in prostate cancer (PC) prognosis and treatments. Maspin, a highly conserved protein throughout evolution, belongs to the serine protease inhibitor (serpin) superfamily. Human maspin is expressed specifically in epithelial cells of several organs. In cancer, maspin correlates with better differentiated phenotypes and better prognoses. Accumulated experimental evidence demonstrates a tumor suppressive role of maspin at the steps of invasion and metastasis. Maspin re-expression in prostate tumor cells induces re-differentiation. Furthermore, maspin specifically sensitizes tumor cells, but not normal cells, to induced apoptosis. Interestingly, however, in our preliminary studies, a paradoxical role of maspin was observed: maspin enhanced tumor cell resistance to stress stimuli. A better understanding of the underlying molecular mechanisms of maspin is clearly called for in order to explore its therapeutic potential. It was realized only recently that maspin is the most deviant member in the serpin superfamily and has a unique conformational plasticity. This new revelation helps explain several lines of evidence generated from our lab including that maspin acts as a serine protease inhibitor-like molecule to inhibit serine protease-like targets such as pro-urokinase type plasminogen activator (uPA) and histone deacetylase 1 (HDAC1). The effect of maspin on HDAC1 is tied to its apoptosis-sensitizing effect. It is worth noting that despite the significant success in recent years in the synthesis of small molecular weight HDAC inhibitors, maspin is the only endogenous polypeptide HDAC inhibitor identified thus far. In the meantime, intracellular maspin has been shown also to interact with heatshock protein 90 (Hsp90) and glutathione S-transferase p isoform (GSTp). While maspin increases cellular GST activity, GSTp seems to be required in maspin-mediated HDAC1 inhibition. Interestingly, maspin inhibited HDAC1-mediated Hsp90 deacetylation, leading to cell resistance to stress imposed by Hsp90 inhibitors. Taken together, our data led to a novel hypothesis that maspin may regulate the balance of survival and death of prostate epithelial cells by inhibiting HDAC1-mediated deacetylation of both histones and Hsp90, in a GSTp-dependent manner. Our hypothesis suggests, for the first time, a biochemical model that links HDAC1, Hsp90 and GSTp to maspin. It further suggests that by inhibiting HDAC1 in a GSTp-dependent manner, maspin may significantly incapacitate Hsp90-dependent oncogenic/survival signaling, strengthen the redox circuitry to neutralize reactive oxygen species generated through hypoxia or oxidative stress, and potentiate the cells to readily commit self-elimination when apoptosis executing signals are emitted in the tissue microenvironment. To test this hypothesis, we will address four Specific Aims.
Aim 1 : To investigate the maspin effects on HDAC1 in transcription regulation and Hsp90 activity.
Aim 2 : To investigate the effect of GSTp on maspin activity.
Aim 3 : To investigate the maspin effects on prostate epithelial drug sensitivity and resistance.
Aim 4 : To validate the maspin molecular partnerships as markers for PC diagnosis and prognosis. The loss of maspin and GSTp marks poor differentiation and poor prognoses of PC. On the other hand, both HDAC1 and Hsp90 are targeted by synthetic inhibitors in experimental cancer therapies. Our hypothesis suggests, for the first time, a biochemical model that links HDAC1, Hsp90 and GSTp to maspin. The dynamics of these complex partnerships is the focus of the current application. The expected results are likely to establish the clinical relevance and functional significance of our novel hypothetical model, which is likely to have a paradigm-shifting impact regarding the therapeutic potential of maspin in PC prognosis and treatment.
Maspin is an evolutionarily conserved serpin with a unique conformational plasticity, and unique epithelial-specific biological functions through its """"""""exotic"""""""" partnerships with histone deacetylase 1 (HDAC1), glutathione S-transferase (GSTp), and heat shock protein (Hsp90). Our preliminary data and current literature support a new paradigm that maspin may protect prostate epithelial differentiation by inhibiting HDAC1 in a GSTp-dependent manner. To our knowledge, maspin is the first endogenous HDAC1 inhibitor ever identified. Furthermore, our evidence is the first to suggest that HDAC1, Hsp90 and GSTp are functionally connected, by maspin. Although the molecular partnerships of each molecule implicated in our model may be complex, the essence of this model suggests that the inhibitory interaction of maspin with HDAC1 may block histone acetylation and upregulate the expression of HDAC1 target genes, whereas the inhibition of HDAC1-mediated Hsp90 deacetylation by maspin may desensitize cells to Hsp90-dependent signal transduction, which is increased in tumor progression. Induction of HDAC1 target genes such as Bax and p21 may preserve the sensitivity of epithelial cells to apoptotic signals. Another HDAC1 target gene regulated by maspin is GSTp that may function to minimize oxidative stress-induced damages both by detoxifying reactive oxygen species (ROS) and by reducing disulfide bridges of specific proteins. The effect of maspin on GSTp in the regulation of ROS and ROS/hypoxia-dependent gene expression would simultaneously protect the epithelial cell integrity and curtail inflammatory stromal reactivities. On the other hand, the dependence of maspin on GSTp in inhibiting HDAC1 suggests for the first time that gene HDAC1-dependent gene transcriptional regulation and Hsp90-activity may respond directly to oxidative stress signals. Our new mechanistic model is strongly supported by the differential expression patterns and the biological activities of maspin in prostate tumor progression. More importantly, this model raises several new possibilities for maspin-based therapeutic intervention of prostate cancer (PC). The expression of maspin and its partnerships may help predict PC prognosis and stratify PC patients for treatments that target distinct mechanisms. Specifically, co-expression of maspin and GSTp in PC cells may confer sensitivity to drugs that directly activate the apoptosis machinery, and resistance to drugs that target Hsp90 or Hsp90-dependent signal transduction pathways. It is worth noting that HDAC inhibitors, particularly HDAC1-specfic inhibitors, may avert the balancing act of maspin in favor of apoptosis. Recombinant maspin or pharmacological induction of maspin expression may be used in combination to treat invasive carcinoma where endogenous maspin is down-regulated or lost. Although both maspin and GSTp may be lost in high grade carcinoma, re-expression of maspin may not suffer for lacking the cognate GSTp. As shown by our preliminary data, maspin re-expression may lead to the up-regulation of GSTp. These possibilities will be the focus of the current application. Specifically, we will investigate the maspin effects on HDAC1 in gene transcription regulation and Hsp90 activity, the effect of GSTp on maspin activity and the maspin effects on prostate epithelial drug sensitivity and resistance. We also plan to validate the maspin molecular partnerships as markers for PC diagnosis and prognosis. The loss of maspin and GSTp marks poor differentiation and poor prognoses of PC. On the other hand, both HDAC1 and Hsp90 are targeted by synthetic inhibitors in experimental cancer therapies. Our hypothesis suggests, for the first time, a biochemical model that links HDAC1, Hsp90 and GSTp to maspin. The dynamics of these complex partnerships is the focus of the current application. The expected results are likely to establish the clinical relevance and functional significance of our novel hypothetical model, which is likely to have a paradigm-shifting impact regarding the therapeutic potential of maspin in PC prognosis and treatment.
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