Comparative expression of the mitotic regulators SAK and PLK in colorectalcancer

Background: Disruption of normal mechanisms for cell cycle regulation is im portant in carcinogenesis. SAK and PLK are members of the polo family of se rine threonine kinases, which in lower organisms have been shown to be requ ired for the precise regulation of mitosis. Studies of human polo family me mbers have focused on PLK, which has been found to be overexpressed in seve ral tumor types, with the degree of overexpression correlating with adverse clinical outcome. However, PLK expression had not previously been analyzed in colorectal cancer. SAK, a polo family member with unique properties, ha d not been systematically studied in any tumor type. Methods: In this study, SAK expression was evaluated in a series of sporadi c human colorectal cancer specimens (n = 74) and compared with that of PLK. Expression was assessed by reverse transcription-polymerase chain reaction . Results: In the majority of cases, both SAK and PLK were more highly expres sed in tumor tissue than in adjacent normal intestinal mucosa. Levels of SA K and PLK expression in tumor relative to paired normal mucosa correlated d irectly with patient age and with each other but did not correlate with tum or stage. These results suggest a mechanism for augmented disruption of mit otic regulation in older patients. Conclusions: The polo family mitotic regulators SAK and PLK are both aberra ntly expressed in colorectal cancer. The potential prognostic significance of SAK and PLK expression in colorectal cancer will be evaluated in the fut ure.