Deciphering the Phospho-Signaling Network Associated with the Linker Region of Multidrug Resistance Protein 1

The ATP-binding cassette subfamily C member 1 (ABCC1) is a key efflux pump that contributes to multidrug resistance in cancer by exporting chemotherapeutic agents and xenobiotics. Although ABCC1 is clinically important, the phosphorylation-dependent regulatory mechanisms governing its activity remain poorly understood, representing a major knowledge gap. To address this gap, we performed a large-scale integrative analysis of publicly available phosphoproteomic datasets curated from over 3800 PubMed-indexed studies. From 688 high-confidence datasets, we mapped Class I phosphosites on ABCC1 and focused on two predominant sites, S919 and S930, located within the cytoplasmic linker domain. Using phosphosite co-occurrence and co-regulation strategies, we identified phosphorylation events that consistently co-regulate with these key ABCC1 sites across diverse experimental conditions. Through multilevel statistical filtering (Fisher's exact test, p < 0.05), recurrence analysis, and experimental context diversity, we defined a high-confidence co-regulatory network comprising 1266 phosphosites across diverse proteins. Mechanistically, this network reveals coordinated phosphorylation of ABCC1 with its known interacting partners, including PTGES3, FASN, and STX4, as well as functionally associated drug transport proteins such as ABCC4, SLC16A1, and SLC20A2. Functional enrichment analysis further linked the ABCC1-centred phospho-network to carcinogenesis, cell-cycle regulation, and drug resistance pathways, highlighting its systems-level role in cancer biology. From a translational perspective, our findings identify phosphosites within the ABCC1 linker domain as actionable regulatory nodes that may be exploited to modulate transporter function, offering potential strategies to overcome chemoresistance.