Gaudreau-Lapierre, A. | Search bioRxiv

bioRxiv2024

Loss of VHL-mediated pRb regulation promotes clear cell renal cell carcinoma

The von Hippel-Lindau (VHL) tumor suppressor is a component of E3 ubiquitin ligase complexes that target cellular substrates for proteasome-mediated degradation. VHL inactivation by genetic aberrations is observed in most sporadic cases of clear cell renal cell carcinoma (ccRCC). VHL loss leads to constitutive stabilization of E3 ligase targets, including hypoxia inducible factor (HIF), in VHL-associated tumors. HIF stabilization upon VHL loss promotes transactivation of hypoxia responsive genes, which contributes to ccRCC development. However, several HIF-independent VHL targets have also been implicated in the promotion of tumorigenesis. Using proximity labeling to identify proteasomal VHL interactors, we identified retinoblastoma protein (pRb) as a novel substrate of VHL. Mechanistically, VHL interacts with pRb in an oxygen-sensitive manner, promoting its ubiquitin-mediated degradation. Concordantly, VHL-inactivation results in pRb hyperstabilization. Functionally, the hyperstabilization of pRb in ccRCC promoted tumorigenesis in vitro and in mouse models. We also show that downstream transcriptional changes induced by pRb hyperstabilization may contribute to ccRCC tumor development. Together, our findings reveal a novel VHL-related pathway which can be therapeutically targeted to inhibit ccRCC tumor development.

cancer biology↗

bioRxiv2022

SPECC1L binds MYPT1/PP1β and can regulate its distribution between microtubules and filamentous actin

The subcellular localization, activity and substrate specificity of the serine/threonine protein phosphatase 1 catalytic subunit (PP1 cat) is mediated through its dynamic association with regulatory subunits in holoenzyme complexes. While some functional overlap is observed for the three human PP1cat isoforms, they also show distinct targeting based on relative preferences for specific regulatory subunits. A well-known example is the preferential association of MYPT1 with PP1{beta} in the myosin phosphatase complex. In smooth muscle, MYPT1/ PP1{beta} counteracts the muscle contraction induced by phosphorylation of the light chains of myosin by the myosin light chain kinase. This phosphatase complex is also found in non-muscle cells, where it is targeted to both myosin and non-myosin substrates and contributes to regulation of the balance of cytoskeletal structure and motility during cell migration and division. Although it remains unclear how MYPT1/PP1{beta} traffics between microtubule- and actin-associated substrates, our identification of the microtubule- and actin-binding protein SPECC1L in both the PP1{beta} and MYPT1 interactomes suggested that it may be the missing link. Validation of their association, together with the strong overlap that we observed for the SPECC1L and MYPT1 interactomes, suggested that they exist in a stable complex in the cell. We further showed that SPECC1L binds MYPT1 directly, and that it can impact the balance of the distribution of the MYPT1/ PP1{beta} complex between the microtubule and filamentous actin networks.

cell biology↗