Serine/threonine kinase that regulates several signal transduction pathways (PubMed:14645249, PubMed:16495336, PubMed:16704422, PubMed:17709393, PubMed:18286207, PubMed:18617507, PubMed:20679487). Isoform 1 modulates the stress response to hypoxia and cytokines, such as interleukin-1 beta (IL1B) and this is dependent on its interaction with MAPK8IP1, which assembles mitogen-activated protein kinase (MAPK) complexes (PubMed:17709393). Inhibition of signal transmission mediated by the assembly of MAPK8IP1-MAPK complexes reduces JNK phosphorylation and JUN-dependent transcription (PubMed:18286207). Phosphorylates 'Thr-18' of p53/TP53, histone H3, and may also phosphorylate MAPK8IP1 (PubMed:16704422). Phosphorylates BANF1 and disrupts its ability to bind DNA and reduces its binding to LEM domain-containing proteins (PubMed:16495336). Down-regulates the transactivation of transcription induced by ERBB2, HRAS, BRAF, and MEK1 (PubMed:20679487). Blocks the phosphorylation of ERK in response to ERBB2 and HRAS (PubMed:20679487). Can also phosphorylate the following substrates that are commonly used to establish in vitro kinase activity: casein, MBP and histone H2B, but it is not sure that this is physiologically relevant (PubMed:14645249). {ECO:0000269|PubMed:14645249, ECO:0000269|PubMed:16495336, ECO:0000269|PubMed:16704422, ECO:0000269|PubMed:17709393, ECO:0000269|PubMed:18286207, ECO:0000269|PubMed:18617507, ECO:0000269|PubMed:20679487}. [Isoform 2]: Phosphorylates 'Thr-18' of p53/TP53, as well as histone H3. Reduces p53/TP53 ubiquitination by MDM2, promotes p53/TP53 acetylation by EP300 and thereby increases p53/TP53 stability and activity. . This is the function of Ensembl gene identifier ENSG00000028116 (VRK2, VRK serine/threonine kinase 2).