Biology subjects

Saffi, G. T.

Publications and source records attributed to Saffi, G. T..

4 recordsLinked to original sources

bioRxiv2026

Inositol Polyphosphate-4-Phosphatase Type II promotes gemcitabine resistance in pancreatic ductal adenocarcinoma cells via lysosomal exocytosis

Chemotherapy resistance is a major challenge in pancreatic ductal adenocarcinoma (PDAC). While high Inositol Polyphosphate-4-Phosphatase Type II (INPP4B) expression correlates with poor outcomes, its function in chemotherapy response is unclear. We show that INPP4B promotes gemcitabine resistance by enhancing lysosomal exocytosis. Across PDAC models, high INPP4B linked to reduced gemcitabine sensitivity, while knockdown restored it. INPP4B also conferred cross-resistance to agents including irinotecan, oxaliplatin, paclitaxel, and daunorubicin. Mechanistically, INPP4B increased cell-surface LAMP1, enhanced extracellular gemcitabine release, and mitigated DNA damage. Pharmacological targeting of lysosomes with chloroquine (CQ), Bafilomycin A (BafA), or specific PIKfyve or TRPML1 inhibitors blocked exocytosis and reversed resistance in vitro. Moreover, chloroquine co-treatment restored gemcitabine sensitivity in INPP4B-overexpressing xenografts. These results establish INPP4B-driven lysosomal exocytosis as a key mechanism of gemcitabine resistance, highlighting a therapeutic target for PDAC resensitization.

cancer biology↗

bioRxiv2021

PIKfyve inhibition reveals a novel role for Inpp4b in the regulation of PtdIns(3)P and lysosome dynamics

Lysosome membranes contain diverse phosphoinositide (PtdIns) lipids that co-ordinate lysosome function and dynamics. The PtdIns repertoire on lysosomes is tightly regulated by the action of diverse PtdIns kinases and phosphatases. Specific roles for PtdIns in lysosomal function and dynamics are currently unclear and require further investigation. PIKfyve, a lipid kinase which synthesizes PtdIns(3,5)P2 from PtdIns(3)P, controls lysosome "fusion-fission" cycles dynamics, autophagosome turnover and endocytic cargo delivery. We have recently characterized a role for INPP4B, a PtdIns phosphatase which hydrolyses PtdIns(3,4)P2 to form PtdIns(3)P, in the regulation of lysosomal biogenesis and function. To gain a better understanding of PtdIns homeostasis on lysosomes, we investigated the consequence of disrupting PIKfyve in Inpp4b-deficient mouse embryonic fibroblasts. Surprisingly, simultaneous inhibition of Inpp4b and PIKfyve functions impair lysosome "fission" dynamics and thereby exacerbate lysosome enlargement, inhibit autophagic flux. Further examination into the underlying processes that may explain exaggerated lysosome enlargement revealed elevated levels of lysosome associated PtdIns(3)P as contributing factors that control lysosome morphology in cells where Inpp4b and PIKfyve are disrupted. Overall, our study suggests that lysosomal functions are regulated by Inpp4b, through a paradoxical role in suppressing the induction of PtdIns(3)P production. SUMMARY STATEMENTIn this study we identify a novel crosstalk between Inpp4b and PIKfyve. This crosstalk regulates lysosome membrane phosphoinositide composition and lysosomal homeostasis. Our data demonstrate that Inpp4b restricts VPS34-dependent induction of PtdIns(3)P levels, which is activated upon apilimod-mediated PIKfyve inhibition. Through this mechanism, Inpp4b contributes to the regulation of lysosomal membrane dynamics and homeostasis.

cell biology↗

bioRxiv2021

INPP4B promotes leukemia by restricting leukemic stem cell differentiation through regulation of lysosomal functions

Signaling pathways that control vital features of leukemic stem cells including multipotency, self-renewal, clonal expansion and quiescence remain unclear. Emerging studies illustrate critical roles for lysosomes in hematopoietic and leukemic stem cell fate. By investigating consequences of INPP4B alterations in AML, we have discovered its role in driving leukemic stemness. We observed that INPP4B is highly expressed leukemic stem cell populations and Inpp4b-deficeint leukemias demonstrate increased disease latency, reduced leukemia initiating potential which is associated with a differentiated leukemic phenotype. Molecular analyses show that Inpp4b-deficient leukemias have compromised lysosomal gene expression, lysosomal content, and lysosomal activity. Our discovery of a novel pathway linking INPP4B, lysosomal biogenesis and leukemic stemness, provides a mechanism to explain the association of high INPP4B expression with poor AML prognosis, and highlights novel patient stratification strategies and LSC-specific leukemic therapies. Key PointsOur findings highlight a novel pathway linking INPP4B, lysosomal function and leukemic stemness that explains the prognostic role of INPP4B in AML. Our data reveal the utility of INPP4B as a biomarker of aggressive AML and provide a rationale to explore INPP4B and its associated function in lysosome biology as novel strategies to target LSC and AML

cancer biology↗

bioRxiv2019

Reactive oxygen species rescue lysosome coalescence during PIKfyve inhibition

Lysosomes are terminal, degradative organelles of the endosomal pathway that undergo repeated fusion-fission cycles with themselves, endosomes, phagosomes, and autophagosomes. Lysosome number and size depends on balanced fusion and fission rates. Thus, conditions that favour fusion over fission can reduce lysosome numbers while enlarging their size. Conversely, favouring fission over fusion may cause lysosome fragmentation and increase their numbers. PIKfyve is a phosphoinositide kinase that generates phosphatidylinositol-3,5-bisphosphate to modulate lysosomal functions. PIKfyve inhibition causes an increase in lysosome size and reduction in lysosome number, consistent with lysosome coalescence. This is thought to proceed through reduced lysosome reformation and/or fission after fusion with endosomes or other lysosomes. Previously, we observed that photo-damage during live-cell imaging prevented lysosome coalescence during PIKfyve inhibition. Thus, we postulated that lysosome fusion and/or fission dynamics are affected by reactive oxygen species (ROS). Here, we show that ROS generated by various independent mechanisms all impaired lysosome coalescence during PIKfyve inhibition and accelerated lysosome fragmentation during re-activation. However, depending on the ROS species or mode of production, lysosome dynamics were affected distinctly. H2O2 impaired lysosome motility and reduced lysosome fusion with phagosomes, suggesting that H2O2 reduces lysosome fusogenecity. In comparison, inhibitors of oxidative phosphorylation, glutathione, and thioredoxin that produce superoxide, did not impair lysosome motility but instead promoted clearance of actin puncta on lysosomes formed during PIKfyve inhibition. Additionally, actin depolymerizing agents prevented lysosome coalescence during PIKfyve inhibition. Thus, we discovered that ROS can generally prevent lysosome coalescence during PIKfyve inhibition using distinct mechanisms depending on the type of ROS.

cell biology↗