Synj2, also known as synaptojanin 2, encodes an inositol polyphosphate phosphatase. It functions in recycling neurotransmitter vesicles, is implicated in spermatogenesis, and plays a role in tethering Pink1 mRNA to mitochondria for local mitophagy [2,5,7]. It is also involved in pathways like protein digestion and absorption, extracellular matrix-receptor interaction, and is associated with immune cell infiltration [1].

In multiple cancers including lung squamous cell carcinoma (LUSC), papillary thyroid carcinoma (PTC), gastric cancer (GC), and hepatocellular carcinoma (HCC), SYNJ2 is highly expressed and promotes cancer progression. In LUSC, overexpressed SYNJ2 predicts poor prognosis and its cancer-promoting effect may be related to certain pathways [1]. In PTC, it may promote progression through angiogenesis and epithelial-mesenchymal transition (EMT) pathways [3]. In GC, it promotes cell metastasis and angiogenesis by up-regulating GRB2 [4]. In HCC, increased SYNJ2 expression may accelerate its occurrence and development via metabolic perturbation pathways [8]. Additionally, a SYNJ2 variant rs9365723 is associated with colorectal cancer risk in the Chinese Han population [6].

In conclusion, Synj2 is essential for neurotransmitter vesicle recycling, spermatogenesis, and local mitophagy. Its dysregulation is closely associated with the development and progression of multiple cancers, highlighting its potential as a biomarker and therapeutic target for cancer treatment.