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Comparative Expression of the Mitotic Regulators SAK and PLK in Colorectal Cancer

From the Departments of Surgery (JCM, CJS), Molecular and Medical Genetics (JWH, JWD), and Clinical Epidemiology (SB), Samuel Lunenfeld Research Institute and Mount Sinai Hospital, University of Toronto, Toronto, Canada.

Correspondence: Address correspondence and reprint requests to: Carol J. Swallow, 600 University Avenue, Suite 1224, Toronto, Ontario, Canada M5G 1X5; Fax: 416-586-8392.

Background: Disruption of normal mechanisms for cell cycle regulation is important in carcinogenesis. SAK and PLK are members of the polo family of serine threonine kinases, which in lower organisms have been shown to be required for the precise regulation of mitosis. Studies of human polo family members have focused on PLK, which has been found to be overexpressed in several 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, had not been systematically studied in any tumor type.

Methods: In this study, SAK expression was evaluated in a series of sporadic 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 expressed in tumor tissue than in adjacent normal intestinal mucosa. Levels of SAK and PLK expression in tumor relative to paired normal mucosa correlated directly with patient age and with each other but did not correlate with tumor stage. These results suggest a mechanism for augmented disruption of mitotic regulation in older patients.

Conclusions: The polo family mitotic regulators SAK and PLK are both aberrantly expressed in colorectal cancer. The potential prognostic significance of SAK and PLK expression in colorectal cancer will be evaluated in the future.

Key Words: Polo kinase • Mitosis • Cell cycle • Colorectal cancer

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