Molecular basis of the regulation of Beclin 1-dependent autophagy by the γ-herpesvirus 68 Bcl-2 homolog M11

Abstract

[ Autophagy 4:8, 989-997; 16 November 2008]; ©2008 Landes Bioscience γ-Herpesviruses (γHVs), including important human pathogens such as Epstein Barr virus, Kaposi's sarcoma-associated HV, and the murine γHV68, encode homologs of the antiapoptotic, cellular Bcl-2 (cBcl-2) to promote viral replication and pathogenesis. The precise molecular details by which these proteins function in viral infection are poorly understood. Autophagy, a lysosomal degradation pathway, is inhibited by the interaction of cBcl-2s with a key autophagy effector, Beclin 1, and can also be inhibited by γHV Bcl-2s. Here we investigate the γHV68 M11-Beclin 1 interaction in atomic detail, using biochemical and structural approaches. We show that the Beclin 1 BH3 domain is the primary determinant of binding to M11 and other Bcl-2s, and this domain binds in a hydrophobic groove on M11, reminiscent of the binding of different BH3 domains to other Bcl-2s. Unexpectedly, regions outside of, but contiguous with, the Beclin 1 BH3 domain also contribute to this interaction. We find that M11 binds to Beclin 1 more strongly than do KSHV Bcl-2 or cBcl-2. Further, the differential affinity of M11 for different BH3 domains is caused by subtle, yet significant, variations in the atomic details of each interaction. Consistent with our structural analysis, we find that Beclin 1 residues L116 and F123, and M11 residue pairs G86 + R87 and Y60 + L74, are required for M11 to bind to Beclin 1 and downregulate autophagy. Thus, our results suggest that M11 inhibits autophagy through a mechanism that involves the binding of the Beclin 1 BH3 domain in the M11 hydrophobic surface groove.

The Beclin 1 network regulates autophagy and apoptosis

“…vBcl-2 of g-herpesviruses including KSHV and M11 can inhibit autophagy via a direct interaction with Beclin 1 (Pattingre et al 31 ). The M11 has higher affinity to Beclin 1 when compared with other vBcl-2 (Ku et al 15 ; Sinha et al 66 ). The herpes simplex virus protein ICP34.5 interacts with Beclin 1 to block double-stranded RNA-activated protein kinase R-dependent macroautophagy induction, which limits neurovirulence by HSV-1 (Orvedahl et al 67 ).…”

Autophagy: for better or for worse

“…Other viruses, such as gamma-herpes virus and human cytomegalovirus, possess B-cell lymphoma-2 (Bcl-2)-like proteins or activate the mTOR signaling pathway to render the cells less sensitive to autophagy induction [99][100][101]. Interestingly, when Toll-like (TLR) and NOD-like (NLR) receptors recognize pathogen-associated molecular patterns, they not only regulate pro-inflammatory cytokine production but can also stimulate autophagy.…”

Bcl-2 complexed with Beclin-1 maintains full anti-apoptotic function

“…BH3-only proteins are pro-apoptotic regulators of apoptosis, the binding of which to anti-apoptotic Bcl-2 members is one mechanism of facilitating the activation of Bax/Bak, crucial mediators of the mitochondrial pathway of apoptosis (Scorrano and Korsmeyer, 2003;Certo et al, 2006;Adams and Cory, 2007). Like other BH3-only proteins, the BH3 domain of Beclin-1 binds to anti-apoptotic Bcl-2 family proteins within their hydrophobic groove (Feng et al, 2007;Oberstein et al, 2007;Maiuri et al, 2007b;Ku et al, 2008;Sinha et al, 2008). Thus, in reconstituted systems it is displaced from Bcl-2/-xL/-w by Bad, tBid or the BH3-mimetic compound, ABT737, though not by Bax/Bak (Erlich et al, 2007;Maiuri et al, 2007b).…”