Osteopontin and its downstream carcinogenic molecules: regulatory mechanisms and prognostic value in cancer progression

Osteopontin (OPN) is a multifunctional phosphorylated glycoprotein that is expressed at significantly elevated levels in various cancers. OPN overexpression is closely associated with the development of cancer progression such as proliferation, metastasis, angiogenesis, apoptosis resistance, drug resistance, and immunosuppression, and may also be an independent prognostic biomarker for a variety of cancers. This review broadly summarizes the mechanisms that regulate the expression of downstream oncogenic molecules after OPN binds to integrin receptors or CD44 receptors, which involve a complex intracellular "signaling traffic network" (including key kinases, signaling pathways, and transcription factors). In addition, we review the prognostic value of OPN, OPN synergistic downstream oncogenic molecules in the female breast, non-small cell lung, prostate, colorectal, gastric, and hepatocellular carcinomas. The prognostic value of OPN in tissues or blood may vary due to differences in study subjects or detection methods, and this aspect of the study requires further systematization with a view to applying the detection of OPN to clinical applications. Importantly, based on the fact that the oncogenic effect of OPN correlates with the expression of the above-mentioned oncogenic molecules, this work may provide some help in the study of combination therapy targeting OPN and the above-mentioned oncogenic molecules.