RRM1 and glioblastoma: The phosphorylation level of the S459 locus within the RRM4 domain of PTBP1 was higher than that in normal tissues in almost all primary tumor tissues except GBM (Fig. 4a–g, i, all P < .05), followed by the S141 locus within the RRM1 domain for colon cancer, ovarian cancer, UCEC, and GBM (Fig. 4a, c–e, h, all P < .05), which also exhibited increased phosphorylation levels.