Figure 3. BNIP3L and Beclin1 overexpression in fibroblasts drives a loss of Cav-1 expression, and promotes tumor growth. To investigate the involvement of stromal BNIP3L and Beclin1 in tumor formation, we stably overexpressed both genes in hTERT fibroblasts. Lv- represents fibroblasts transduced with the vector alone control, namely Lv-105 (puro). (A) Note that BNIP3L and Beclin1 overexpression in fibroblasts is sufficient to induce a loss of Cav-1 expression, as observed by immunoblot analysis. Blotting with β-actin is shown as a control for equal protein loading. (B) BNIP3-, Beclin1- or control- fibroblasts were co-injected with MDA-MB-231 epithelial breast cancer cells, into the flanks of nude mice. At 4 weeks post-injection, the mice were sacrificed and the tumors were collected. n = 10 per experimental group. For both BNIP3L- and Beclin1 fibroblasts, a significant increase in tumor growth was observed. Thus, overexpression of both autophagic genes (BNIP3L and Beclin1) is sufficient to drive tumor growth.