Integrin Alpha2beta 1 (α2β1) Promotes Prostate Cancer Skeletal Metastasis

Men who die of prostate cancer (PCa) do so because of systemic metastases, the most frequent of which are within the skeleton. Recent data suggest that the colonization of the skeleton is mediated in part by collagen type I, the most abundant protein within the bone. We have shown that enhanced collagen I binding through increased expression of integrin α2β1 stimulated in vitro invasion and promoted the growth of PCa cells within the bone. Accordingly, we sought to determine whether α2β1 integrin is a potential mediator of skeletal metastasis. To examine whether α2β1 integrin mediates PCa metastasis, α2 integrin was over-expressed in low-tumorigenic LNCaP PCa cells or selectively knocked-down in highly metastatic LNCaPcol PCa cells. We document that the over-expression of α2 cDNA stimulated whereas α2 shRNA inhibited the ability of transduced cells to bind to or migrate towards collagen in vitro. Correspondingly, α2 integrin knock-down reduced the tumor burden of intra-osseous tumors compared to control-transduced cells. To investigate the clinical significance of α2β1 expression in PCa, α2β1 protein was measured in prostatic tissues and in soft tissue and bone metastases. The data demonstrate that α2β1 protein was elevated in PCa skeletal metastases compared to either PCa primary lesions or soft tissue metastases suggesting that α2β1 contributes to the selective metastasis to the bone. Taken together, these data support that α2β1 integrin is needed for the efficient metastasis of PCa cells to the skeleton.