A positive feedback DNA-PK/MYT1L-CXCR1-ERK1/2 proliferative autocrine loop in the progression of glioblastoma

Glioblastoma is the most common primary brain tumor in adults. Our previous studies revealed a functional interplay of a myelin transcription factor 1-like (MYT1L) with the DNA-dependent protein kinase (DNA-PK) in the regulation of p21 transcription. However, a contributing role of this functional interplay in the progression of glioblastoma remains largely unknown. Here, we used cell lines with normal DNA-PK (M059K) or deficient DNA-PK (M059J) as a model system to demonstrate the importance of the DNA-PK-dependent activation of MYT1L in controlling the transcription of CXC chemokine receptor 1 (CXCR1) in a positive-feedback chemokine proliferative autocrine loop in glioblastoma progression. In normal DNA-PK cells, MYT1L acted as an oncogene by promoting cell proliferation, inhibiting apoptosis, and shortening a cell cycle S phase. However, in DNA-PK-deficient cells, MYT1L functioned as a tumor suppressor by inhibiting cell proliferation and inducing a G1 arrest. The enforced expression of MYT1L promoted CXCR1 transcription in DNA-PK-normal cells but the attenuated transcription in DNA-PK-deficient cells. Bioinformatics analysis predicted a MYT1L-binding sequence at the CXCR1 promoter. The functional dependence of MYT1L on DNA-PK in CXCR1 transcription was validated by luciferase assay. Although the expression of CXCR1 was lower in M059J cells as compared to M059K cells, it was higher than in normal brain tissue. Our findings also show that CXCR1 ligands interleukin 8 (IL8) and GRO protein alpha (GROalpha) overexpressed in M059J and M059K cells may signal through the extracellular signal-regulated kinase 1/2 (ERK1/2) pathway that can be blocked by CXCR1 siRNA. Our findings demonstrate the existence of autocrine positive feedback DNA-PK/MYT1L-CXCR1-ERK1/2 proliferation loop in glioblastoma cells, that may represent a target loop for therapeutic intervention.