Cbl-b, a RING-type E3 ubiquitin ligase, targets phosphatidylinositol 3-kinase for ubiquitination in T cells.
Cbl-b is implicated in setting the threshold of T lymphocyte activation. In Cbl-b-deficient T cells, the activation of Vav, a guanine nucleotide exchange factor, is significantly enhanced. The molecular mechanism underlying Cbl-b-regulated Vav activation was unclear. Here it is shown that Cbl-b interacts with and induces ubiquitin conjugation to the p85 regulatory subunit of phosphatidylinositol 3-kinase, an upstream regulator of Vav. A functional RING finger of Cbl-b was essential for p85 ubiquitination. However, a loss of function mutation at the well-conserved amino-terminal variant src homology (SH) 2 domain of Cbl-b did not affect its ligase activity. A distal carboxyl-terminal proline-rich region in Cbl-b was mapped to contain the primary binding sequences for the SH3 domain of p85. Deletion of either the distal proline-rich region in Cbl-b or the SH3 domain of p85 severely reduced ubiquitin conjugation to p85. The data suggest a molecular link for Cbl-b-mediated negative regulation of Vav, with phosphatidylinositol 3-kinase as a direct target for Cbl-b E3 ubiquitin ligase.
Fang
D
D
Division of Cell Biology, La Jolla Institute for Allergy and Immunology, San Diego, CA 92121, USA.
Wang
H Y
HY
Fang
N
N
Altman
Y
Y
Elly
C
C
Liu
Y C
YC
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins / Q000737:chemistry / Q000502:physiology*; D006801:Humans; D019169:Jurkat Cells; D008025:Ligases / Q000502:physiology; D019869:Phosphatidylinositol 3-Kinases / Q000737:chemistry / Q000378:metabolism*; D010750:Phosphoproteins / Q000737:chemistry / Q000502:physiology*; D011392:Proline / Q000378:metabolism; D017434:Protein Structure, Tertiary; D050721:Proto-Oncogene Proteins c-cbl; D013601:T-Lymphocytes / Q000201:enzymology* / Q000276:immunology*; D044767:Ubiquitin-Protein Ligases; D014452:Ubiquitins / Q000378:metabolism*; D018909:src Homology Domains
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D010750:Phosphoproteins; D014452:Ubiquitins; D011392:Proline; C492211:CBLB protein, human; D050721:Proto-Oncogene Proteins c-cbl; D044767:Ubiquitin-Protein Ligases; D019869:Phosphatidylinositol 3-Kinases; D008025:Ligases