# KSHV reprograms host RNA splicing via FAM50A to activate STAT3 and drive oncogenic cellular transformation

## TL;DR

This study shows how KSHV, a virus linked to cancer, uses a protein called FAM50A to alter RNA splicing and promote cancer development.

## Contribution

The study reveals a novel mechanism by which KSHV manipulates host splicing machinery through FAM50A to drive oncogenesis.

## Key findings

- FAM50A is crucial for KSHV-induced cellular transformation and tumorigenesis.
- FAM50A knockout disrupts SHP2 splicing and reduces STAT3 activation in KSHV-infected cells.
- KSHV reprograms RNA splicing to alter pathways involved in vascular permeability and metabolism.

## Abstract

RNA alternative splicing is a fundamental cellular process implicated in cancer development. Kaposi’s sarcoma-associated herpesvirus (KSHV), the etiological agent of multiple human malignancies, including Kaposi’s sarcoma (KS), remains a significant concern, particularly in AIDS patients. A CRISPR-Cas9 screening of matched primary rat mesenchymal stem cells (MM) and KSHV-transformed MM cells (KMM) identified key splicing factors involved in KSHV-induced cellular transformation. To elucidate the mechanisms by which KSHV-driven splicing reprogramming mediates cellular transformation, we performed transcriptomic sequencing, identifying 131 differentially alternative spliced transcripts, with exon skipping as the predominant event. Notably, these transcripts were enriched in vascular permeability, multiple metabolic pathways, and ERK1/2 signaling cascades, which play key roles in KSHV-induced oncogenesis. Further analyses of cells infected with KSHV mutants lacking latent genes, including vFLIP, vCyclin, and viral miRNAs, as well as cells overexpressing LANA, revealed their involvement in alternative splicing regulation. Among the identified splicing factors, FAM50A, a component of the spliceosome complex C, was found to be crucial for KSHV-mediated transformation. FAM50A knockout resulted in distinct splicing profiles in both MM and KMM cells and significantly inhibited KSHV-driven proliferation, cellular transformation, and tumorigenesis. Consistently, FAM50A knockdown suppressed the proliferation of PEL cells. Mechanistically, FAM50A knockout altered SHP2 splicing, promoting an isoform with enhanced enzymatic activity that led to reduced STAT3 Y705 phosphorylation in KMM cells. These findings reveal a novel paradigm in which KSHV hijacks host splicing machinery, specifically FAM50A-mediated SHP2 splicing, to sustain STAT3 activation and drive oncogenic transformation.

Kaposi’s sarcoma-associated herpesvirus (KSHV) causes cancers such as Kaposi’s sarcoma, particularly in AIDS patients. This study uncovers how KSHV hijacks a fundamental cellular process called RNA splicing to promote cancer development. We identified key splicing events that alter critical pathways involved in vascular permeability, metabolism, and oncogenic signaling, particularly ERK1/2 and STAT3. A specific protein, FAM50A, was found to be essential for KSHV-driven cancerous transformation. Removing FAM50A disrupted splicing, weakening cancer-promoting signals. These findings provide new insights into how viruses manipulate host cells to drive cancer and highlight RNA splicing as a potential target for future therapies.