Ppip5k2, or Diphosphoinositol Pentakisphosphate Kinase 2, is an inositol pyrophosphate kinase. It interconverts 5-IP7 and IP8, key members of the inositol pyrophosphate cell-signaling family, and functions at the interface of cell signaling and bioenergetic homeostasis [6]. Its kinase activity has reversible nature, along with unique ligand-stimulated ATPase activity and substrate traveling between two ligand-binding sites [5].

In multiple disease conditions, Ppip5k2 shows significant effects. In colorectal carcinoma (CRC), it is highly expressed and promotes pathogenesis by facilitating DNA homologous recombination repair independent of its kinase activity. S1006 dephosphorylation leads to its nuclear translocation, enhancing DNA repair ability of CRC cells [1]. In non-small lung cancer (NSCLC), it facilitates proliferation and metastasis through the AKT/mTOR signaling pathway [3]. In ovarian cancer, a LncRNA (LncOVM) stabilizes Ppip5k2, promoting complement C5 secretion, which attracts myeloid-derived suppressor cells (MDSCs) in the tumor microenvironment to facilitate metastasis [7]. In a four-generation family, potential variants in Ppip5k2 were identified as candidate genetic contributors to familial keratoconus (KC). Gene-trap mouse models showed corneal phenotypes resembling KC, such as irregular corneal surfaces and thinning [2]. In three Ppip5k2 mouse models, CCT decreased, pachymetry maps revealed abnormal thinning, slit lamp examinations showed corneal abnormalities, and histological analysis showed epithelial thickening and stromal layer damage [4]. Mutations in Ppip5k2 in humans and mice are associated with hearing loss. Mouse models with a targeted deletion of the Ppip5k2 phosphatase domain exhibit cochlear outer hair cell degeneration and elevated hearing thresholds [6].

In conclusion, Ppip5k2 plays crucial roles in multiple biological processes and disease conditions. Its functions in facilitating DNA repair, promoting cancer cell proliferation and metastasis, and its association with KC and hearing loss are well-demonstrated through various in vivo and functional studies, especially with the help of gene-trap and knockout mouse models. These studies provide potential therapeutic targets for related diseases.