Genetic variations of the midkine (MK) gene in human sporadic colorectal and gastric cancers.

Midkine (MK), a retinoic acid responsible protein, is regulated during development and may play an important role in tumorigenesis. A search for genetic variations of the MK gene, located on chromosome 11q11.2 in humans, has not yet been conducted in cancers. To examine the entire coding region, as well as 4 regions of the promoter covering all functional motifs, 8 sets of intron-based and promoter region primers were designed. Using these primers, polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) analysis of genomic DNA samples from 60 sporadic colorectal and 37 sporadic gastric cancer patients was carried out. This analysis, followed by DNA sequencing, revealed a heterozygous g/t polymorphism at the 62nd base on intron 3 in five colorectal tumors (8.3%) and one gastric tumor (2.7%). In the promoter region, a heterozygous CTT deletion, creating a (CTTTT)2 repeat, in one colorectal cancer sample (1.67%) and a heterozygous 2-bp deletion in the G7 tract in another colorectal cancer patient were detected. A/G and A/A alleles were also detected at nt. -1741 in 36 (97.3%) and one (2.7%) gastric cancer samples, respectively. The A/G alleles were observed in all colorectal cancer patients (100%). All variations observed in the promoter region showed polymorphism. These results suggest that in sporadic colorectal and gastric cancers some gene alterations are present in the MK promoter region, but alterations in the coding region are rare.