Removal of the BH4 Domain from Bcl-2 Protein Triggers an Autophagic Process that Impairs Tumor Growth12

• Published in: Neoplasia (New York, N.Y.) N.Y.), 2013-03, Vol.15 (3), p.315-327
• Main Authors: Trisciuoglio, Daniela, De Luca, Teresa, Desideri, Marianna, Passeri, Daniela, Gabellini, Chiara, Scarpino, Stefania, Liang, Chengyu, Orlandi, Augusto, Del Bufalo, Donatella
• Format: Article
• Language: English
• ISSN: 1522-8002; 1476-5586

Here, we show that forced expression of a B-cell lymphoma 2 (bcl-2) protein lacking residues 1 to 36 at the N-terminal, including the entire Bcl-2 homology 4 (BH4) domain, determines reduction of in vitro and in vivo human melanoma growth. Noteworthy, melanoma cells in vivo exhibit markedly increased autophagy, as response to expression of bcl-2 protein deleted of its BH4 domain. This observation led to the identification of a novel gain of function for bcl-2 protein lacking the BH4 domain. In particular, upon different autophagic stimuli in vitro , overexpression of bcl-2 protein deleted of BH4 domain induces autophagosome accumulation, conversion of microtubule-associated protein 1 light chain 3B-II, reduced expression of p62/SQSTM1 protein, and thereby enhanced autophagic flux. The relevance of Beclin-1 is evidenced by the fact that 1) the autophagy-promoting and growth-inhibiting properties are partially rescued by Beclin-1 knockdown in cells expressing bcl-2 protein lacking the BH4 domain, 2) Beclin-1 only interacts with wild-type but not with deleted bcl-2, and 3) BH4 domain removal from bcl-2 protein does not influence in vitro and in vivo growth of tumor cells expressing low levels of endogenous Beclin-1. These results provide new insight into molecular mechanism of bcl-2 functions and represent a rationale for the development of agents interfering with the BH4 domain of bcl-2 protein.