Bag-3 expression is involved in pathogenesis and progression of colorectal carcinomas.

Bcl-2-associated athanogene 3 (Bag-3) belongs to a member of the Hsc70 binding co-chaperone Bag-family proteins and has critical roles in protein homeostasis, cell survival, actin organization, cell adhesion, cell motility and tumor metastasis. To clarify the role of Bag-3 in colorectal carcinogenesis and subsequent development, its expression was examined by immunohistochemistry (IHC) and in situ hybridization (ISH) on tissue microarrays containing colorectal carcinomas, adenomas, non-neoplastic mucosa (NNM) and metastatic carcinomas in lymph node and liver. Colorectal carcinoma tissue and cell lines were studied for Bag-3 expression by RT-PCR, Western blot and immunofluorescence. The results demonstrated that Bag3 was distinctly expressed in Colo201, Colo205, DLD-1, HCT-15, HCT-116, HT-29, KM-12, SW480, SW620, and WiDr at both mRNA and protein levels. Carcinoma showed stronger Bag-3 expression than adjacent NNM by IHC and Western blot (P<0.05), while its mRNA had the opposite by real-time PCR and ISH (P<0.05). Metastatic carcinoma more frequently expressed Bag-3 mRNA in lymph node and liver than in primary carcinoma (P<0.05). Immunohistochemically, Bag-3 expression was seen to gradually decrease from carcinoma, adenoma to NNM (P<0.05). There was a positive correlation between Bag-3 expression and TNM staging and GRP94 expression (P<0.05), but no relationship to patient age or sex, tumor size, depth of invasion, lymphatic or venous invasion, lymph node metastasis, differentiation or prognosis of colorectal carcinomas (P<0.05). Our study indicated that aberrant Bag-3 expression might be involved in colorectal adenoma-adenocarcinoma sequence and subsequent progression.