Regulatory elements present in the promoter of a gene drive the expression of the gene in response to various stimuli. Lemur Tyrosine Kinase 2 (LMTK2) is a membrane-anchored Serine/Threonine kinase involved in endosomal protein trafficking and androgen signaling amongst other processes. Previous studies have shown this protein to be of therapeutic importance in cystic fibrosis and prostate cancer. However, nothing is known about the endogenous expression of this protein and its regulation. In this study, we analyzed the gene encoding human LMTK2, to look for possible regulatory elements that could affect its expression. Interestingly, the human lmtk2 gene contains a consensus TPA (12- O-Tetradecanoylphorbol-13-acetate)-responsive element (TRE) in the region preceding its start codon. The element with the sequence TGAGTCA modulates LMTK2 expression in response to treatment with TPA, a synthetic Protein Kinase C (PKC) activator. It serves as the binding site for c-Fos, a member of the Activator Protein -1 (AP-1) transcription factor complex, which is transactivated by PKC. We observed that TPA, at low concentrations, increases the promoter activity of LMTK2, which leads to a subsequent increase in the mRNA transcript and protein levels. This modulation occurs through binding of the AP-1 transcription factor complex to the lmtk2 promoter. Thus, our current study has established LMTK2 as a TPA-responsive element-containing gene, which is upregulated downstream of PKC activation. Considering the involvement of LMTK2 in intracellular processes as well as pathological conditions, our findings demonstrate a way to modulate intracellular LMTK2 levels pharmacologically for potentially therapeutic purposes.
Keywords: 4α-TPA, 4α-phorbol 12, 13-didecanoate; ACD, Actinomycin D; AP-1 complex; AP-1, Activator Protein – 1; Chx, Cycloheximide; GM-CSF, Granulocyte Macrophage Colony Stimulating Factor; LMTK2; LMTK2, Lemur Tyrosine Kinase 2; PKC activation; PKC, Protein Kinase C; Phorbol ester; Promoter; SEAP, Secretory Alkaline Phosphatase; TPA, Phorbol 12-myristate 13-acetate; TPA-responsive element; TRE, TPA-response element.