Biology subjects

Cryns, V. L.

Publications and source records attributed to Cryns, V. L..

9 recordsLinked to original sources

bioRxiv2025

Lipid Transfer Proteins and PI4KIIα Generate a Phosphoinositide-Linked Proteome

Phosphoinositide (PIPn) lipid second messengers in membranes regulate a myriad of cellular processes. In the cytosol, the phosphatidylinositol (PI) 3-kinase (PI3K)/Akt pathway is scaffolded on IQGAP1 to facilitate the activation of Akt by the synthesis of PI3,4,5P3. In the nucleus, PIPn signaling occurs in regions devoid of membranes via their stable association with proteins. While several of these proteins have been identified, understanding the extent and impact of protein-linked PIPn signaling warrants further investigation. The tumor suppressor p53, was shown in the companion paper to be regulated by PI transfer proteins (PITPs) and a PI 4-kinase (PI4KII), which are required to form p53-PIPn complexes that assemble a nuclear PI3K/Akt pathway. Here we report that class I PITPs (PITP/{beta}) and PI 4-kinase initiate PIPn linkages to many different proteins. PITP/{beta} and PI4KII accumulate in the nucleoplasm in response to stress and are necessary to synthesize nuclear PIPns linked to proteins. These PITP/{beta}-dependent protein-PIPn complexes are detected by metabolically labeling cells with the PIPn precursor [H3]-myo-inositol and resist denaturation and SDS-PAGE, indicating that these protein-PIPn complexes represent a putative posttranslational modification. Proteomic analyses of proteins that are regulated by PITP/{beta} and/or are linked to PI4,5P2 have identified an emerging PIPylome that is enriched in metabolic, signaling, cytoskeletal and DNA repair pathway components. Taken together, these data provide evidence for an emerging proteome with linked PIPns that represent a PIPn signaling paradigm that is distinct from the membrane-localized pathway but utilizes many of the same PIP kinases and phosphatases. In briefPhosphatidylinositol transfer proteins and PI 4-kinase initiate a PIPn-linked protein network in membrane-free regions.

cell biology↗

bioRxiv2025

Regulation of the MDM2-p53 Nexus by a Nuclear Phosphoinositide and Small Heat Shock Protein Complex

The tumor suppressor p53 maintains genome stability in the setting of cellular stress and is frequently mutated in cancer. The stability of p53 is regulated by its interaction with the oncoprotein MDM2, a ubiquitin E3 ligase. Recently, nuclear phosphoinositides were reported to bind and stabilize p53. Here, we report that genotoxic stress induces the type I phosphatidylinositol phosphate kinase (PIPKI) and its product phosphatidylinositol 4,5-bisphosphate (PIP2) to bind and regulate the stability and function of MDM2. Following genotoxic stress, nuclear PIPKI binds to MDM2 to generate a complex of MDM2 and PIP2. PIP2 binding to MDM2 differentially regulates the recruitment of the small heat shock proteins (sHSPs) B-crystallin (BC) and HSP27 to the MDM2-PIP2 complex, acting as an on-off switch that regulates MDM2 stability, downstream targets, ubiquitination activity, and interaction with p53. Our results demonstrate an unexpected role for nuclear phosphoinositides conferring specificity to the MDM2-PIP2-sHSPs association. Notably, the differential engagement of BC and HSP27 reveals that sHSPs are not merely passive chaperones but play active, selective roles in fine-tuning MDM2 function and MDM2-p53 nexus. These findings provide a novel therapeutic strategy for targeting this pathway in cancer.

cancer biology↗

bioRxiv2024

Regulation of the poly(A) Polymerase Star-PAP by a Nuclear Phosphoinositide Signalosome

Star-PAP is a noncanonical poly(A) polymerase that controls gene expression. Star-PAP was previously reported to bind the phosphatidylinositol 4-phosphate 5-kinase PIPKI and its product phosphatidylinositol 4,5-bisphosphate, which regulate Star-PAP poly(A) polymerase activity and expression of specific genes. Recent studies have revealed a nuclear PI signaling pathway in which the PI transfer proteins PITP/{beta}, PI kinases and phosphatases bind p53 to sequentially modify protein-linked phosphatidylinositol phosphates and regulate its function. Here we demonstrate that multiple phosphoinositides, including phosphatidylinositol 4-monophosphate and phosphatidylinositol 3,4,5-trisphosphate are also coupled to Star-PAP in response to stress. This is initiated by PITP/{beta} binding to Star-PAP, while the Star-PAP-linked phosphoinositides are modified by PI4KII, PIPKI, IPMK, and PTEN recruited to Star- PAP. The phosphoinositide coupling enhances the association of the small heat shock proteins HSP27/B-crystallin with Star-PAP. Knockdown of the PITPs, kinases, or HSP27 reduce the expression of Star-PAP targets. Our results demonstrate that the PITPs generate Star-PAP-PIPn complexes that are then modified by PI kinases/phosphatases and small heat shock proteins that regulate the linked phosphoinositide phosphorylation and Star-PAP activity in response to stress.

cell biology↗

bioRxiv2024

Enhanced PI3K/Akt Signaling in Response to p85α Loss is Regulated by Endosomal PI3Kα and PI3P

PI3K is a heterodimer of p110 catalytic subunit and p85 adaptor subunit that is activated by agonist-stimulated receptor tyrosine kinases. Although the interaction of p85 with activated receptors recruits p110 to membranes, studies have demonstrated that p85 loss, which occurs commonly in cancer, paradoxically promotes agonist-stimulated PI3K/Akt signaling. We recently demonstrated that p110 localizes to microtubules via MAP4, facilitating its interaction with activated receptor kinases in endosomes to initiate PI3K/Akt signaling. Here, we demonstrate that in response to agonist stimulation and p85 knock down the residual p110, coupled predominantly to p85{beta}, exhibits enhanced microtubule localization, MAP4 binding and interaction with endosomal receptor tyrosine kinases, thereby augmenting PI3K/Akt signaling. The interaction of the C2 domain of p110 with PI3P is required for recruiting p110 into endomembranes and enhancing PI3K/Akt signaling. These findings provide a mechanism for the augmented agonist-stimulated PI3K/Akt signaling upon p85 loss and point to novel therapeutic targets for cancer. IN BRIEFThis study provides the comprehensive mechanism for p85 loss induced and receptor tyrosine kinase stimulated PI3K/Akt signaling.

cell biology↗

bioRxiv2023

Heme biosynthesis regulates BCAA catabolism and thermogenesis in brown adipose tissue

With age, people tend to accumulate body fat and reduce energy expenditure1. Brown (BAT) and beige adipose tissue dissipate heat and increase energy expenditure via the activity of the uncoupling protein UCP1 and other thermogenic futile cycles2,3. The activity of brown and beige depots inversely correlates with BMI and age4-11, suggesting that promoting thermogenesis may be an effective approach for combating age-related metabolic disease12-15. Heme is an enzyme cofactor and signaling molecule that we recently showed to regulate BAT function16. Here, we show that heme biosynthesis is the primary contributor to intracellular heme levels in brown adipocytes. Inhibition of heme biosynthesis leads to mitochondrial dysfunction and reduction in UCP1. Although supplementing heme can restore mitochondrial function in heme-synthesis-deficient cells, the downregulation of UCP1 persists due to the accumulation of the heme precursors, particularly propionyl-CoA, which is a product of branched-chain amino acids (BCAA) catabolism. Cold exposure promotes BCAA uptake in BAT, and defects in BCAA catabolism in this tissue hinder thermogenesis17. However, BCAAs contribution to the TCA cycle in BAT and WAT never exceeds 2% of total TCA flux18. Our work offers a way to integrate current literature by describing heme biosynthesis as an important metabolic sink for BCAAs.

cell biology↗

bioRxiv2023

Regulation of NRF2 by Phosphoinositides and Small Heat Shock Proteins

Reactive oxygen species (ROS) are generated by aerobic metabolism, and their deleterious effects are buffered by the cellular antioxidant response, which prevents oxidative stress. The nuclear factor erythroid 2-related factor 2 (NRF2) is a master transcriptional regulator of the antioxidant response. Basal levels of NRF2 are kept low by ubiquitin-dependent degradation of NRF2 by E3 ligases, including the Kelch-like ECH-associated protein 1 (KEAP1). Here, we show that the stability and function of NRF2 is regulated by the type I phosphatidylinositol phosphate kinase {gamma} (PIPKI{gamma}), which binds NRF2 and transfers its product phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2) to NRF2. PtdIns(4,5)P2 binding recruits the small heat shock protein HSP27 to the complex. Silencing PIPKI{gamma} or HSP27 destabilizes NRF2, reduces expression of its target gene HO-1, and sensitizes cells to oxidative stress. These data demonstrate an unexpected role of phosphoinositides and HSP27 in regulating NRF2 and point to PIPKI{gamma} and HSP27 as drug targets to destabilize NRF2 in cancer. In briefPhosphoinositides are coupled to NRF2 by PIPKI{gamma}, and HSP27 is recruited and stabilizes NRF2, promoting stress-resistance.

cancer biology↗

bioRxiv2023

Lipid transfer proteins initiate nuclear phosphoinositide signaling

Phosphoinositide (PIPn) messengers are present in non-membranous regions of nuclei where they are assembled into a phosphatidylinositol (PI) 3-kinase (PI3K)/Akt pathway that is distinct from the cytosolic membrane-localized pathway. In the nuclear pathway, PI kinases/phosphatases bind the p53 tumor suppressor protein (wild-type and mutant) to generate p53-PIPn complexes (p53-PIPn signalosome) that activate Akt by a PI3,4,5P3-dependent mechanism in non-membranous regions of the nucleus. This pathway is dependent on a source of nuclear PIPns that is poorly characterized. Here we report that a subset of PI transfer proteins (PITPs), which transport PI between membranes to enable membrane-localized PIPn synthesis, also interact with p53 in the nucleus upon genotoxic stress. Class I PITPs (PITP/{beta}) specifically supply the PI required for the generation of p53-PIPn complexes and subsequent signaling in the nucleus. Additionally, the PI 4-kinase PI4KII binds to p53 and the PITPs to catalyze the formation of p53-PI4P. p53-PI4P is then sequentially phosphorylated to synthesize p53-PIPn complexes that regulate p53 stability, nuclear Akt activation and genotoxic stress resistance. In this way, PITP/{beta} and PI4KII bind p53 and collaborate to initiate p53-PIPn signaling by mechanisms that require PI transfer by PITP/{beta} and the catalytic activity of PI4KII. Moreover, the identification of these critical upstream regulators of p53-PIPn signaling point to PITP/{beta} and PI4KII as potential therapeutic targets in this pathway for diseases like cancer. In BreifPhosphatidylinositol transfer proteins and a PI 4-kinase initiate nuclear p53-PIPn signaling in membrane-free regions.

cell biology↗

bioRxiv2021

A p53-Phosphoinositide Signalosome Regulates Nuclear Akt Activation

The tumor suppressor p53 and the phosphoinositide 3-kinase (PI3K)-Akt pathway have fundamental roles in regulating cell growth, apoptosis and are frequently mutated in cancer. Here, we show that genotoxic stress induces nuclear Akt activation by a p53-dependent mechanism that is independent from the canonical membrane-localized PI3K-Akt pathway. Upon genotoxic stress a nuclear p53-PI3,4,5P3 complex is generated in regions devoid of membranes by a nuclear PI3K, and this complex recruits all the kinases required to activate Akt and phosphorylate FOXOs, inhibiting DNA damage-induced apoptosis. Wild-type p53 activates nuclear Akt in an on/off fashion upon stress, whereas mutant p53 stimulates high basal Akt activity, indicating a fundamental difference. The nuclear p53-phosphoinositide signalosome is distinct from the canonical membrane-localized pathway and insensitive to PI3K inhibitors currently in the clinic, underscoring its therapeutic relevance. In briefp53 assembles a PI3K-Akt pathway that regulates nuclear Akt activation independent of the canonical pathway on membranes.

cell biology↗

bioRxiv2019

Methyl-Metabolite Depletion Elicits Adaptive Responses to Support Heterochromatin Stability and Epigenetic Persistence

S-adenosylmethionine (SAM) is the methyl-donor substrate for DNA and histone methyltransferases that regulate cellular epigenetic states. This metabolism-epigenome link enables the sensitization of chromatin methylation to altered SAM abundance. However, a chromatin-wide understanding of the adaptive/responsive mechanisms that allow cells to actively protect epigenetic information during life-experienced fluctuations in SAM availability are unknown. We identified a robust response to SAM depletion that is highlighted by preferential cytoplasmic and nuclear de novo mono-methylation of H3 Lys 9 (H3K9) at the expense of global losses in histone di- and tri-methylation. Under SAM-depleted conditions, de novo H3K9 mono-methylation preserves heterochromatin stability and supports global epigenetic persistence upon metabolic recovery. This unique chromatin response was robust across the mouse lifespan and correlated with improved metabolic health, supporting a significant role for epigenetic adaptation to SAM depletion in vivo. Together, these studies provide the first evidence for active epigenetic adaptation and persistence to metabolic stress.

biochemistry↗