An Alternative Splice Variant of HIPK2 with Intron Retention Contributes to Cytokinesis

Abstract

HIPK2 is a DYRK-like kinase involved in cellular stress response pathways, development, and cell division. Two alternative splice variants of HIPK2, HIPK2-FL and HIPK2-Δe8, have been previously identified as having different protein stability but similar functional activity in the stress response. Here, we describe one additional HIPK2 splice variant with a distinct subcellular distribution and functional activity in cytokinesis. This novel splice variant lacks the last two exons and retains intron13 with a stop codon after 89 bp of the intron, generating a short isoform, HIPK2-S, that is detectable by 2D Western blots. RT-PCR analyses of tissue arrays and tumor samples show that HIPK2-FL and HIPK2-S are expressed in normal human tissues in a tissue-dependent manner and differentially expressed in human colorectal and pancreatic cancers. Gain- and loss-of-function experiments showed that in contrast to HIPK2-FL, HIPK2-S has a diffuse, non-speckled distribution and is not involved in the DNA damage response. Rather, we found that HIPK2-S, but not HIPK2-FL, localizes at the intercellular bridge, where it phosphorylates histone H2B and spastin, both required for faithful cell division. Altogether, these data show that distinct human HIPK2 splice variants are involved in distinct HIPK2-regulated functions like stress response and cytokinesis.

Functions ofSRPK,CLKandDYRKkinases in stem cells, development, and human developmental disorders

“…• ER-stress response via IRE1a-ASK1-JNK [279] • UV stress-induced apoptosis [249] • DNA damage response and apoptosis [83,84,153,154] • Non-apoptotic functions in cytokinesis regulation [96][97][98] interacting proteins involved with RNA processing than other CMGC kinases [89]. Non-catalytic functions of nuclear SRPK1 in splicing regulation have also been proposed.…”

“…For CLKs, non‐splicing functions include kinase activation of phosphatases and regulation of cytokinesis [ 94 , 95 ]. Similarly, non‐apoptotic functions of HIPKs have been described in regulating cytokinesis [ 96 , 97 , 98 ], alongside facilitation of p53‐independent apoptosis [ 99 ]. Together, these suggest exciting opportunities to identify novel functions and biology that are controlled by these interesting kinase families.…”

“…HIPK2 co‐localises at the midbody with Histone H2B following recruitment by Aurora B and phosphorylates Histone H2B at S14, which is required for successful cytokinesis [ 96 , 98 ]. Similarly, an alternative isoform of HIPK2 (short ‘‐S’ form, following intron 13 retention and translation of a shorter protein lacking part of the auto‐inhibitory domain) is required for cytokinesis, with depletion of the short form resulting in fewer cells completing abscission, leading to increased binucleation [ 97 ].…”

HIPK2 Is Required for Midbody Remnant Removal Through Autophagy-Mediated Degradation

“…HIPK2-mediated phosphorylation of the extrachromosomal histone H2B (ecH2B) at Ser14 is not required for its midbody localization but contributes to the formation of the abscission site and is essential for successful cytokinesis (Rinaldo et al, 2012;Monteonofrio et al, 2019). HIPK2-mediated phosphorylation of the microtubule severing enzyme Spastin at Ser268 is required for its midbody localization to cut microtubules and the subsequent physical separation of the two daughter cells (Pisciottani et al, 2019;Gatti et al, 2020).…”