MAP/Microtubule Affinity Regulating Kinase 4 (MARK4)

Sequence analysis predicted that the 752-amino acid MARKL1 protein, 62% identical to MARK3, contains an N-terminal serine/threonine kinase domain, a central ubiquitin-associated domain, and a C-terminal KA1 -associated kinase domain. A smaller transcript, MARKL1S, lacking exon 16 and the KA1-associated kinase domain in the 688-amino acid protein, was also detected exclusively in brain. RT-PCR analysis detected upregulated expression in nearly all clinical hepatocellular carcinoma cells. Northern blot analysis revealed ubiquitous expression of a 3.6-kb transcript, with highest expression in testis. Immunofluorescence microscopy demonstrated homogeneous cytoplasmic expression. Colony-forming assays showed that MARKL1 antisense reduced the growth of SNU475 cells.