Biology subjects

Erpapazoglou, Z.

Publications and source records attributed to Erpapazoglou, Z..

3 recordsLinked to original sources

bioRxiv2024

A neural alternative splicing program controls cellular function and growth in Pancreatic Neuroendocrine tumours

Pancreatic neuroendocrine tumours (PanNETs) are a rare heterogeneous group of neoplasms that arise from pancreatic islet cells. The hormone secreting function of pancreatic neuroendocrine cells is altered in PanNETs, rendering these tumours functional or non-- functional (secreting excessive or lower levels of hormones, respectively). Genome wide approaches have revealed the genomic landscape of PanNETs but have not shed light on this problematic hormone secretion. In the present work, we show that alternative splicing (AS) deregulation is responsible for changes in the secretory ability of PanNET cells. We reveal a group of alternative microexons that are regulated by the RNA binding protein SRRM3 and are preferentially included in mRNAs in PanNET cells, where SRRM3 is also upregulated. These microexons are part of a larger neural program regulated by SRRM3. We show that their inclusion gives rise to protein isoforms that change stimulus-induced secretory vesicles and their trafficking in PanNET cells. Moreover, the increased inclusion of these microexons results in an enhanced neuronal component in PanNET tumours. Using knock-down and splicing switching oligonucleotides in cellular and animal PanNET models, we show that decrease of the SRRM3 levels or even of the inclusion levels of the three most deregulated microexons can significantly alter the PanNET cell characteristics. Collectively, our study links secretory impairment and nerve dependency to alternative splicing deregulation in PanNETs, providing promising therapeutic targets for PanNET treatment.

cancer biology↗

bioRxiv2022

Communication between the nucleus and the mitochondria via NDUFS4 alternative splicing in gastric cancer cells

A constant communication between the nucleus and the mitochondria allows both organelles to ensure cellular homeostasis and adaptation to mitochondrial stress. Mitochondrial biogenesis and function are controlled by anterograde regulatory pathways involving a large number of nuclear-encoded proteins. Transcriptional networks controlling the nuclear-encoded mitochondrial genes are known, however alternative splicing (AS) regulation has not been implicated in this communication. Here, we show that IQGAP1, a scaffold protein that regulates AS of distinct subsets of genes in gastric cancer cells, participates in AS regulation that strongly affects mitochondrial respiration. Combined proteomic analyses and RNA-seq profiles of IQGAP1KO and parental cells show that IQGAP1KO alters a specific AS event of the mitochondrial respiratory chain complex I subunit NDUFS4 and downregulates a subset of complex I subunits. In IQGAP1KO cells, respiratory complex I intermediates accumulate resembling assembly deficiencies observed in patients with Leigh syndrome bearing NDUFS4 mutations. Mitochondrial complex I activity is significantly lower in KO compared to parental cells, while exogenous expression of IQGAP1 partially restores NDUFS4 AS pattern and expression and reverses mitochondrial defects of IQGAP1KO cells. Our work sheds light to a novel facet of IQGAP1 in mitochondrial quality control that involves fine-tuning of complex I activity through AS regulation.

molecular biology↗

bioRxiv2020

Nuclear IQGAP1 promotes gastric cancer cell growth by altering the splicing of a cell-cycle regulon in co-operation with hnRNPM

In response to oncogenic signals, Alternative Splicing (AS) regulators such as SR and hnRNP proteins show altered expression levels, subnuclear distribution and/or post-translational modification status, but the link between signals and these changes remains unknown. Here, we report that a cytosolic scaffold protein, IQGAP1, performs this task in response to heat-induced signals. We show that in gastric cancer cells, a nuclear pool of IQGAP1 acts as a tethering module for a group of spliceosome components, including hnRNPM, a splicing factor critical for the response of the spliceosome to heat-shock. IQGAP1 controls hnRNPMs sumoylation, subnuclear localization and the relevant response of the AS machinery to heat-induced stress. Genome-wide analyses reveal that IQGAP1 and hnRNPM co-regulate the AS of a cell cycle-related RNA regulon in gastric cancer cells, thus favouring the accelerated proliferation phenotype of gastric cancer cells. Overall, we reveal a missing link between stress signals and AS regulation.

molecular biology↗