Biology subjects

Trinkle-Mulcahy, L.

Publications and source records attributed to Trinkle-Mulcahy, L..

5 recordsLinked to original sources

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↗

bioRxiv2022

Subcellular distribution of PP1 isoforms in holoenzyme complexes

Unlike its counterpart Ser/Thr kinases, the predominant Ser/Thr protein phosphatase 1 (PP1) is a promiscuous enzyme that gains its subcellular localization and substrate specificity from a large panel of regulatory proteins with which it associates in predominantly dimeric complexes. Inhibition of specific PP1-mediated dephosphorylation events relies on targeting the regulatory rather than the catalytic subunit, which in turn relies on a comprehensive understanding of the holoenzyme complexes that underlie its distribution throughout the cell. Proteomic, bioinformatic and biochemical screens have assembled lists of putative regulatory proteins, which have been studied to varying degrees. We took a non-biased approach to link steady-state localization to complexes, using a combination of fluorescence imaging, cellular fractionation and quantitative affinity purification/mass spectrometry (AP/MS) to map interactomes for PP1[a]/{beta}/{gamma} in 3 human cell lines. Comparing the distribution of each isoform between the pool of identified regulatory subunits highlighted key signaling pathways and identified c20orf27 as a novel PP1 regulatory protein. Steady-state association of a large fraction of PP1 with the evolutionarily conserved SDS22 was demonstrated, as was redistribution at the entry to mitosis. This is consistent with recent work suggesting that SDS22 acts as a PP1 sink from which it can be recruited as needed. Moving forward, this approach can be used to assess the redistribution of PP1 during other cellular processes or in response to perturbations or disease states, facilitating identification of the relevant complexes and the design of strategies to target them therapeutically.

cell biology↗

bioRxiv2022

LRRK2 Phosphorylates Neuronal Elav RNA-Binding Proteins to RegulatePhenotypes Relevant to Parkinson's Disease

Parkinsons disease (PD) is characterized by accumulation of -synuclein and the loss of dopaminergic neurons. Mutations which cause an increase in the kinase activity of Leucine-Rich-Repeat Kinase-2 (LRRK2) are a major inherited cause of PD. Research continues to determine which targets LRRK2 phosphorylates to cause disease. Polymorphisms in the locus of ELAVL4, an RNA-binding protein are a risk-factor for Parkinsons disease and an ELAV family member was identified in Drosophila as required for pathology instigated by human mutant LRRK2. We discovered that three neuronal ELAVs including ELAVL4 (also known as HuD) are phosphorylated by LRRK2. This controls binding of neuronal ELAVs to mRNA and their post- transcriptional regulation of mRNA abundance and splicing in neuronal cell lines and the mouse midbrain. LRRK2 G2019S functionally inhibits neuronal ELAVs effects on mRNA abundance, while enhancing their effects on mRNA splicing. The combination of LRRK2 G2019S and ELAVL4-/- causes accumulation of LRRK2 and -synuclein, loss of dopaminergic neurons and motor deficits. Targets of neuronal ELAVs are also selectively misregulated in cells and tissues of PD patients. Together, this suggests that misregulation of neuronal ELAVs, triggered by LRRK2 mutations may contribute to the characteristic pathology of Parkinsons disease. Brief SummaryLRRK2, a kinase linked to Parkinsons disease, phosphorylates the neuronal ELAV RNA-binding proteins to aggravate key hallmarks of Parkinsons disease including accumulation of -synuclein and motor deficits in mice.

cell biology↗

bioRxiv2018

Regulation of ATR activity by the RNA polymerase II phosphatase PNUTS-PP1

Ataxia telangiectasia mutated and Rad3-related (ATR) kinase is a key factor activated by DNA damage and replication stress. Here, we show that ATR signaling is increased in human cells after depletion of the RNAPII phosphatase PNUTS-PP1, which dephosphorylates RNAPII on Ser 5 of its carboxy-terminal domain (CTD) (pRNAPII S5). Increased ATR signaling was observed in the presence and absence of ionizing radiation or replication stress and even in G1 phase after depletion of PNUTS. Vice versa, ATR signaling was reduced, in a PNUTS dependent manner, after inhibition of the CDK7 kinase mediating pRNAPII S5. Furthermore, CDC73, a well-known RNAPII-CTD binding protein, was required for the high ATR signaling after depletion of PNUTS and co-immunoprecipitated with RNAPII and ATR. These results suggest a novel pathway involving RNAPII, PNUTS-PP1 and CDC73 in ATR signaling and give new insight into the diverse functions of ATR.

cancer biology↗