Bcl-2-like protein 1; Bcl2-L-1; apoptosis regulator Bcl-X (BCL2L1, BCL2L, BCLX)

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Function

depending upon the alternatively spliced form, inhibits (Bcl-XL) or enhances (Bcl-XS) apoptosis
Bcl-XL is a potent inhibitor of cell death
isoform Bcl-XL anti-apoptotic activity is inhibited by association with SIVA isoform 1
inhibits activation of caspases (putative)
appears to regulate cell death by blocking the voltage-dependent anion channnel (VDAC) by binding to it & preventing the release of the caspase activator, cytochrome c, from the mitochondrial membrane
the Bcl-XS isoform promotes apoptosis
proteolytically cleaved by caspases during apoptosis
the cleaved protein, lacking the BH4 motif, has pro-apoptotic activity
Bcl-XL forms homodimers, & heterodimers with BAX, BAK & BCL2
heterodimerization with BAX does not seem to be required for anti-apoptotic activity
also interacts with BAD & BBC3
isoform Bcl-XL binds to Siva isoform 1
interacts with BCL2L11 (putative)
interacts with BECN1 & PGAM5

the BH4 motif is required for anti-apoptotic activity
the BH1 & BH2 motifs are required for both heterodimerization with other Bcl-2 family members & for repression of cell death
belongs to the Bcl-2 family

Bcl-XS is expressed at high levels in cells that undergo a high rate of turnover, such as developing lymphocytes
in contrast, Bcl-XL is found in tissues containing long-lived postmitotic cells, such as adult brain

↑ UniProt http://www.uniprot.org/uniprot/Q07817.html
↑ Boise LH et al bcl-x, a bcl-2-related gene that functions as a dominant regulator of apoptotic cell death. Cell. 1993 Aug 27;74(4):597-608. PMID: https://www.ncbi.nlm.nih.gov/pubmed/8358789