Bimodal effects of bone morphogenetic proteins in prostate cancer.

摘要

This dissertation describes observations made on the effect of bone morphogenetic protein (BMP) signaling in an aggressive human prostate cancer cell line, C4-2B, two murine prostate cancer cell lines, E8 and cE1, derived from the primary site of androgen dependent and recurrent tumors of prostate cancer, respectively, and primary cultures of murine cancer associated fibroblasts (CAFs). We previously described that BMP7 could protect C4-2B cells from serum starvation induced apoptosis by sustaining Survivin expression. We further examine the mechanisms behind BMP7 mediated protection from stress induced apoptosis. When C4-2B cells are treated with BMP7, we find that Survivin promoter activity correlates with Smad activation and is ameliorated by dominant negative Smad5. Furthermore JNK activity is also observed to be sustained by BMP7 treatment in the face of serum starvation and co-treatment with a JNK inhibitor abolished the anti-apoptotic effect of BMP7 in a survivin independent manner. Thus we found that anti-apoptotic activity of BMP7 is mediated by both Smad and JNK, albeit with autonomous mechanisms. Using primary cultures of CAFs, isolated from our conditional Pten deletion model of prostate cancer, we tested the effect of BMP2 and 7, both of which are upregulated during tumor growth. Interestingly, each BMP is able to induce secretion of the cytokine, SDF-1/CXCL12. SDF-1 secretion is correlated with Smad phosphorylation and can be blocked by Noggin treatment. BMP treatment increases pre-spliced SDF-1 mRNA and actinomycin D can block the induced secretion of SDF-1 by BMPs, indicating a transcriptional modulation of SDF-1 expression by BMP. Using human microvascular endothelial cells, we demonstrate that increased SDF-1 levels can stimulate tube formation in vitro, implicating a role in tumor angiogenesis. We also find that BMP can protect CAFs from stress induced apoptosis independent of SDF-1. Thus, the study identifies a novel BMP-SDF-1 signaling axis as well as a protective effect of BMP in CAFs. Finally, we examined the effect of BMP inhibitor, Noggin, on the biology of murine prostate cancer cell lines. In vitro data show that Noggin overexpression in cE1 cells decreases cell proliferation while enhancing cell migration. In contrast the in vivo data show that Noggin overexpression increases the mass of the grafts and Ki67 staining shows increased proliferation. We also transduced CAF cells with Noggin and formed subcutaneous grafts in combination with cE1 or E8 cells. When E8 cells were co-injected with CAF/Noggin, larger tumors lacking glandular structures were produced. In the case of cE1 cells mixed with CAF/Noggin however, tumors grew mostly resembling those with CAF/Control with evidence of decreased CD31 staining. Disparate results seen with cE1/Noggin grafts and cE1 grafts mixed with CAF/Noggin implicate a modulation of Noggin activity by the tumor microenvironment. Similarly, the effect of Noggin released from the CAFs appears to influence the cancer cells differentially based on their differentiation status/origin. The majority of the in vivo data support a role of BMP as tumor suppressor in primary prostate cancer progression. However, BMP is shown to have pro-tumorigenic effects on metastatic cell lines as well as via activation of fibroblasts in the tumor microenvironment on certain hallmarks of cancer progression, such as angiogenesis. The positive and negative effects of BMP thus may be linked to stage-specific aspects of cancer progression, and when better understood, may provide new opportunities to combat prostate cancer.