AB3875 Sigma-AldrichAnti-SUMO1 Antibody

Sumoylation of p53 by the ubiquitin-like protein, SUMO-1/sentrin/PIC1, has been shown to stimulate its transcriptional activation activity. The SUMO E3 ligase, a key enzyme in the recognition of substrates to be sumoylated, has not yet been identified. We isolated PIAS1 (protein inhibitor of activated STAT1) as a SUMO-1 binding protein by yeast two-hybrid screening. In addition, PIAS1 bound p53 and Ubc9, the E2 for SUMO. PIAS1 that was mutated in the RING finger-like domain bound p53 and SUMO-1, but not Ubc9. PIAS1 catalyzed the sumoylation of p53 both in U2OS cells and in vitro in a domain-dependent manner. These data suggest that PIAS1 functions as a SUMO ligase, or possibly as a tightly bound regulator of it, toward p53.

Covalent modification of cellular proteins by the ubiquitin-like modifier SUMO regulates various cellular processes, such as nuclear transport, signal transduction, stress response and cell-cycle progression. But, in contrast to ubiquitylation, sumoylation does not tag proteins for degradation, but seems to enhance their stability or modulate their subcellular compartmentalization.

We have cloned a new human gene, cbl-3, which encodes a protein with marked homology to the cbl family of proteins. The predicted protein encoded by this gene retains the conserved phosphotyrosine binding domain (PTB) in the N-terminal and the zinc finger but is significantly shorter (MW 52.5 kDa) than the other mammalian cbl proteins. The protein lacks the extensive proline rich domain and leucine zipper seen in c-cbl and cbl-b and structurally most resembles the C. elegans and Drosophila cbl proteins. The gene is ubiquitously expressed with highest expression in the aerodigestive tract, prostate, adrenal gland, and salivary gland. The protein is phosphorylated and recruited to the EGFR upon EGF stimulation and inhibits EGF stimulated MAP kinase activation. In comparison to the other mammalian cbl proteins (e.g. cbl-b), cbl-3 interacts with a restricted range of proteins containing Src Homology 3 regions. An alternatively spliced form of the cbl-3 protein was also identified which deletes a critical region of the PTB domain and which does not interact with the EGFR nor inhibit EGF stimulated MAP kinase activation. These data demonstrate that cbl-3, a novel mammalian cbl protein, is a regulator of EGFR mediated signal transduction.