PhD Scientific Days 2026

Poster Session 2.C - Molecular Medicine

The Role of Plasma Membrane Ca²⁺-ATPase 4b in Autophagy

Name of the presenter

Tóth, Sarolta

Institute/workplace of the presenter

Semmelweis University, Department of Transfusion Medicine

Authors

Sarolta Tóth¹, Bence Parragh¹, Réka Nagy¹, Zhanerke Kenzhebayeva², Randa Naffa¹, Ágnes Enyedi¹
1: Department of Transfusion Medicine, Semmelweis University
2: Department of Anatomy, Cell and Developmental Biology, Eotvos Lorand University

Text of the abstract

Introduction: Autophagy is a conserved eukaryotic process that delivers cytoplasmic components to lysosomes for degradation. Lysosomal function depends on Ca²⁺ homeostasis, yet the mechanism responsible for lysosomal Ca²⁺ refilling remains unclear. Plasma membrane Ca²⁺-ATPases (PMCAs) regulate cytosolic Ca²⁺ levels, but their potential intracellular roles are poorly understood.

Aims: We aimed to determine whether the PMCA4b isoform localizes to autophagic compartments and functions as a Ca²⁺ pump that contributes to lysosomal Ca²⁺ refilling.

Method: Human cell lines (HEK293, MCF-7) expressing tagged PMCA4b were subjected to autophagy induction (starvation, chloroquine, rapamycin). Colocalization with the autophagic marker LC3 and the lysosomal marker Lamp1 was analyzed by fluorescence microscopy while protein expression levels were determined by Western blotting. In vivo studies were performed in Drosophila melanogaster to analyze PMCA expression and localization following autophagic induction.

Results: PMCA4b undergoes internalization upon autophagy induction and localizes to LC3- and Lamp1-positive compartments, and its expression increases the abundance of autophagic structures. We found that the LLL1167–1169 motif in the C-terminal regulatory tail of PMCA4b is required for its recruitment to autolysosomal structures. The essential auxiliary subunit of PMCAs, CD147 accompanies PMCA4b during autophagy whereas in the absence of PMCA4b, CD147 is retained at the plasma membrane. Consistent with these findings, the PMCA ortholog dmPMCA is upregulated during starvation in Drosophila and shows strong colocalization with autolysosomal markers.

Conclusion: Our findings identify PMCA4b as a candidate regulator of lysosomal Ca²⁺ homeostasis and suggest that altered PMCA4b expression and trafficking may contribute to diseases associated with lysosomal Ca²⁺ dysfunction.

Funding: This work is supported by the 2025-2.1.1-EKÖP-2025-00014 University Research Scholarship Programme of the Ministry for Culture and Innovation from the source of the National Research, Development and Innovation Fund, and by TKP2021-EGA-24.