Unraveling biological processes and EGFR pathway regulation by the protein tyrosine phosphatase PTPRH in non-small cell lung cancer

The delicate balance of protein phosphorylation is often disrupted in cancers, with hyperactivity of kinases and inactivation of phosphatases driving cell proliferation and survival pathways. PTPRH, a protein tyrosine phosphatase, is deregulated or mutated in certain cancers, including non-small cell lung cancer (NSCLC). However, the biological processes that PTPRH is involved in and how they may contribute to tumorigenesis are unknown. Previous studies have linked PTPRH to the regulation of the EGFR pathway but the full extension of this regulation and the underlying mechanisms remain to be elucidated. We found that PTPRH knockout tends to increase the phosphorylation levels of EGFR at the tyrosine residue 1173 (1197), whereas overexpression of PTPRH wild-type significantly decreases phosphorylation in one of the NSCLC cell lines. Surprisingly, disruption of the extracellular or intracellular domains of the phosphatase leads to EGFR dephosphorylation in a similar manner. Co-immunoprecipitation and proximity-dependent biotinylation (BioID) experiments demonstrated that PTPRH do not directly interact with EGFR, but rather with CDK5RAP3 and EIF2AK2, two proteins reported to regulate the downstream pathway NF-κB. In addition, BioID revealed 55 novel PTPRH interactors in NSCLC cells, which are enrichedin translation and RNA-associated pathways. Guided by RNA sequencing analysis, we observed that overexpression of the phosphatase downregulates multiple oncogenic signature pathways and modulates the gene expression of 34 protein tyrosine phosphatases and 45 tyrosine kinases, EGFR included. Together, these results shed light on the importance of PTPRH in regulating biological and cellular processes and how its inactivation may support cancer progression.