Loss of INPP5K attenuates IP3-induced Ca2+ responses in the glioblastoma cell line U-251 MG cells

Jens Loncke; Tomas Luyten; Ana Raquel Ramos; Christophe Erneux; Geert Bultynck

doi:10.1016/j.bbadva.2023.100105

Loss of INPP5K attenuates IP₃-induced Ca²⁺ responses in the glioblastoma cell line U-251 MG cells

BBA Adv. 2023 Sep 27:4:100105. doi: 10.1016/j.bbadva.2023.100105. eCollection 2023.

Authors

Jens Loncke¹, Tomas Luyten¹, Ana Raquel Ramos², Christophe Erneux², Geert Bultynck¹

Affiliations

¹ Laboratory of Molecular and Cellular Signaling, KU Leuven, Leuven, Belgium.
² ULB, IRIBHM, Campus Erasme, Bâtiment C, 808 Route de Lennik, Bruxelles 1070, Belgium.

Abstract

INPP5K (inositol polyphosphate 5-phosphatase K) is an endoplasmic reticulum (ER)-resident enzyme that acts as a phosphoinositide (PI) 5-phosphatase, capable of dephosphorylating various PIs including PI 4,5-bisphosphate (PI(4,5)P₂), a key phosphoinositide found in the plasma membrane. Given its ER localization and substrate specificity, INPP5K may play a role in ER-plasma membrane contact sites. Furthermore, PI(4,5)P₂ serves as a substrate for phospholipase C, an enzyme activated downstream of extracellular agonists acting on Gq-coupled receptors or tyrosine-kinase receptors, leading to IP₃ production and subsequent release of Ca²⁺ from the ER, the primary intracellular Ca²⁺ storage organelle. In this study, we investigated the impact of INPP5K on ER Ca²⁺ dynamics using a previously established INPP5K-knockdown U-251 MG glioblastoma cell model. We here describe that loss of INPP5K impairs agonist-induced, IP₃ receptor (IP₃R)-mediated Ca²⁺ mobilization in intact cells, while the ER Ca²⁺ content and store-operated Ca²⁺ influx remain unaffected. To further elucidate the underlying mechanisms, we examined Ca²⁺ release in permeabilized cells stimulated with exogenous IP₃. Interestingly, the absence of INPP5K also disrupted IP₃-induced Ca²⁺ release events. These results suggest that INPP5K may directly influence IP₃R activity through mechanisms yet to be resolved. The findings from this study point towards role of INPP5K in modulating ER calcium dynamics, particularly in relation to IP₃-mediated signaling pathways. However, further work is needed to establish the general nature of our findings and to unravel the exact molecular mechanisms underlying the interplay between INNP5K function and Ca²⁺ signaling.

Keywords: Calcium signaling; IP3 receptors; Inositol polyphosphate 5-phosphatase K; PI(4,5)P2.