Stromal Hh pathway activity accelerates prostate tumor growth

4816

Hedgehog (Hh) signaling is an important regulator of prostate development and we have shown previously that Shh over-expression and paracrine activation of stromal Hh pathway activity accelerates LNCaP xenograft tumor growth. In this study, we demonstrate that stromal Hh activity alone is sufficient to accelerate tumor growth. We examined LNCaP proliferation in xenograft tumors made by co-injecting an equal mixture of parental LNCaP and LNCaP cells over-expressing Shh (LNShh) into the flank of nude mice. LNCaP/LNShh mix tumors exhibited significantly increased tumor growth rate compared to tumors made with LNCaP cells alone. Immunohistochemical staining for GFP expressed by LNShh, but not parent LNCaP showed that proliferation was significantly and selectively increased in the parent LNCaP cells rather than the LN-Shh cells. Thus, Shh does not have an autonomous effect only on LNShh cells, but effects proliferation of all LNCaP within a tumor. We then examined the effect of constitutive Hh pathway activity in the tumor stroma. Comparison of immortalized urogenital sinus mesenchymal (UGSM) cells derived from E16 Gli3-/- mice and wild type littermate demonstrated ligand-independent activation of Hh signaling in the Gli3-/- cells. Bi-clonal xenografts composed of LNCaP co-injected with either Gli3-/- or Gli3+/+ UGSM cells were generated to examine the effect of stromal pathway activation on tumor growth. Bi-clonal xenografts containing Gli3-/- UGSM cells exhibited significantly faster growth than tumors containing Gli3+/+ UGSM. These studies show that activation of the Hh pathway in the stroma of LNCaP xenografts is sufficient to accelerate tumor growth and that the paracrine stimulation of growth is not preferentially directed toward cells over-expressing Hh ligand.