SUMO wrestling with Ras

Abstract

This review discusses our current understanding of the small ubiquitin-like modifier (SUMO) pathway and how it functionally intersects with Ras signaling in cancer. The Ras family of small GTPases are frequently mutated in cancer. The role of the SUMO pathway in cancer and in Ras signaling is currently not well understood. Recent studies have shown that the SUMO pathway can both regulate Ras/MAPK pathway activity directly and support Ras-driven oncogenesis through the regulation of proteins that are not direct Ras effectors. We recently discovered that in Ras mutant cancer cells, the SUMOylation status of a subset of proteins is altered and one such protein, KAP1, is required for Ras-driven transformation. A better understanding of the functional interaction between the SUMO and Ras pathways could lead to new insights into the mechanism of Ras-driven oncogenesis.

Keywords: KAP1; KRAS; SUMO; colorectal cancer; non-oncogene addiction.

Figure 1.

Intersection between the Ras and the SUMO pathway in cancer. Ras can be activated by multiple upstream signaling inputs including receptor tyrosine kinases (RTKs), G protein-coupled receptors (GPCRs), calcium influx (Ca²⁺) and the T-cell receptor (TCR) complex. Downstream of Ras, several members of MAPK pathway, including MEK kinases and the transcription factors Ets-1 and Elk-1, are SUMOylated. The SUMO pathway consists of a single E1 ligase (SAE1/SAE2 heterodimer), a single E2 ligase (Ubc9) and several E3 proteins. Through the regulation of KRAS-associated SUMOylated proteins (KASPs) such as KAP1, the SUMO pathway plays a supportive role in KRAS-driven transformation. SUMO modification is reversible by sentrin-specific proteases (SENPs).