UBAP1 Is a Component of an Endosome-Specific ESCRT-I Complex that Is Essential for MVB Sorting

Abstract

Endosomal sorting complexes required for transport (ESCRTs) regulate several events involving membrane invagination, including multivesicular body (MVB) biogenesis, viral budding, and cytokinesis. In each case, upstream ESCRTs combine with additional factors, such as Bro1 proteins, to recruit ESCRT-III and the ATPase VPS4 in order to drive membrane scission. A clue to understanding how such diverse cellular processes might be controlled independently of each other has been the identification of ESCRT isoforms. Mammalian ESCRT-I comprises TSG101, VPS28, VPS37A-D, and MVB12A/B. These could generate several ESCRT-I complexes, each targeted to a different compartment and able to recruit distinct ESCRT-III proteins. Here we identify a novel ESCRT-I component, ubiquitin-associated protein 1 (UBAP1), which contains a region conserved in MVB12. UBAP1 binds the endosomal Bro1 protein His domain protein tyrosine phosphatase (HDPTP), but not Alix, a Bro1 protein involved in cytokinesis. UBAP1 is required for sorting EGFR to the MVB and for endosomal ubiquitin homeostasis, but not for cytokinesis. UBAP1 is part of a complex that contains a fraction of total cellular TSG101 and that also contains VPS37A but not VPS37C. Hence, the presence of UBAP1, in combination with VPS37A, defines an endosome-specific ESCRT-I complex.

VPS37 Isoforms Differentially Modulate the Ternary Complex Formation of ALIX, ALG-2, and ESCRT-I

“…29,30) One report, however, suggests that UBAP1 favors VPS37A when assembling ESCRT-I complexes and functions in the sorting of EGFR to MVB, but not in cytokinesis. 30) This accords with the selective interaction of UBAP1 with HD-PTP, a paralog of ALIX involved in MVB sorting. 31) On the other hand, UBAP1 does not associate with ALIX, 30) which is involved in cytokinesis and virus budding.…”

A Pseudomonas aeruginosa TIR effector mediates immune evasion by targeting UBAP1 and TLR adaptors

“…TNFR1 inhibition was specific to PumA as expression of the Brucella TIR domain‐containing protein BtpA/TcpB did not have any significant effect (Fig EV5B). We therefore carried a yeast two‐hybrid screen to identify an alternative target of PumA and found UBAP1, a key component of the ESCRT‐I mediating trafficking and sorting of ubiquitinated cargo proteins on MVBs (Stefani et al , 2011; Agromayor et al , 2012). This interaction was confirmed by co‐IP from cells co‐expressing PumA and UBAP1 (Fig 6A and B) as well as by pull‐down using purified PumA or PumA 1–136 and cell extracts with either streptavidin‐tagged UBAP1 (Fig 6C) or Myc‐UBAP1 (Appendix Fig S5A).…”

“…We show that PumA directly interacts with both TIRAP and MyD88 to control TLR signalling. Uniquely, it also targets the ubiquitin‐associated protein 1 (UBAP1), a recently discovered component of the endosomal‐sorting complex required for transport I (ESCRT‐I; Stefani et al , 2011). UBAP1 is known to play a key role in selective sorting of ubiquitinated endosomal cargo on multi‐vesicular bodies (MVB), via its interaction with VPS37A and other components of ESCRT‐I namely TSG101 (Wunderley et al , 2014), as well as with the ESCRT regulator, His domain protein tyrosine phosphatase (HDPTP; Stefani et al , 2011).…”

“…Uniquely, it also targets the ubiquitin‐associated protein 1 (UBAP1), a recently discovered component of the endosomal‐sorting complex required for transport I (ESCRT‐I; Stefani et al , 2011). UBAP1 is known to play a key role in selective sorting of ubiquitinated endosomal cargo on multi‐vesicular bodies (MVB), via its interaction with VPS37A and other components of ESCRT‐I namely TSG101 (Wunderley et al , 2014), as well as with the ESCRT regulator, His domain protein tyrosine phosphatase (HDPTP; Stefani et al , 2011). UBAP1 has been shown to control endosomal sorting of ubiquitinated EGFR (Stefani et al , 2011) as well as ubiquitin‐dependent degradation of antiviral surface proteins (Agromayor et al , 2012) and integrins (Kharitidi et al , 2015).…”

“…UBAP1 is known to play a key role in selective sorting of ubiquitinated endosomal cargo on multi‐vesicular bodies (MVB), via its interaction with VPS37A and other components of ESCRT‐I namely TSG101 (Wunderley et al , 2014), as well as with the ESCRT regulator, His domain protein tyrosine phosphatase (HDPTP; Stefani et al , 2011). UBAP1 has been shown to control endosomal sorting of ubiquitinated EGFR (Stefani et al , 2011) as well as ubiquitin‐dependent degradation of antiviral surface proteins (Agromayor et al , 2012) and integrins (Kharitidi et al , 2015). More recently, UBAP1 was shown to modulate steady‐state trafficking of cytokine receptors in non‐stimulated cells (Mamińska et al , 2016).…”