Mutations in the Mucin Binding Domain of the Human Kidney Injury Molecule-1 (KIM-1) Gene Are Present in Renal Epithelial Neoplasms
CM Schworer, PL Zhang, GS Gerhard, F Lin. Geisinger Medical Center, Danville, PA; William Beaumont Hospital, Royal Oak, MI
Background: KIM-1 is a sensitive and specific marker for identifying clear cell renal cell carcinoma (CRCC) and papillary renal cell carcinoma (PRCC). Over-expression of KIM-1 is only frequently observed in both CRCC and PRCC (Lin et al. AJSP 2007;31:371). Recent study showed KIM-1 to be a phosphatidylserine receptor with a phagocytic activity. But the role of over-expression of KIM-1 in RCC is not known. Elevated protein levels could arise as a result of mutations in the KIM-1 coding and/or promoter regions, or perhaps from an epigenetic basis. Alterations in the KIM-1 protein could also play a role in tumor pathophysiology. We therefore performed sequence analysis of the KIM-1 gene in four subtypes of renal epithelial neoplasms, i.e., CRCC, PRCC, ChRCC, and oncocytoma.
Design: Genomic DNA was prepared from paraffin-embedded tumor tissue containing four subtypes of renal tumors. Using the purified DNAs as the template, PCR was performed to amplify each of the nine major coding exons of the KIM-1 gene. Each PCR product then went through the cloning and sequencing process. Vector NTI software was used to compare exon DNA sequence to the published sequence of HAVCR-1 (NM_012206).
Results: No differences in DNA sequence for exons 2, 3, 5, 6, 7, 8, and 9 were encountered among the four subtypes of renal tumors. However, a number of mutations were observed for exon 4, a region of the protein thought to be in KIM-1's mucin-binding domain. The DNA sequence of exon 4 from PRCC agreed exactly with the published sequence of the protein. The reaming three subtypes of renal tumors showed a 15 base deletion in the exon 4. This would translate into a protein lacking a MTTVP stretch of protein. Additional mutations in exon 4 were observed: 1) a T to C mutation resulting in an amino acid change from Leu157 to Pro157; 2) a T to G silent mutation in both ChRCC and CRCC (Thr207); and 3) a double mutation within the same codon (T to G and A to G) in oncocytoma resulting in a change from Thr207 to Ala207.
Conclusions: KIM-1 coding region mutations are present in CRCC but not in PRCC, even though over-expression of KIM-1 is observed in both conditions. Therefore, it seems unlikely that these mutations play a role in the regulation of KIM-1 expression. However, the finding of a 15 base deletion in Exon 4 in CRCC, ChRCC, and oncocytoma suggests that it may play a role in the development and/or progression of these tumors. Further investigation of this finding is of interest.
Category: Genitourinary (including renal tumors)
Wednesday, March 11, 2009 1:00 PM
Poster Session VI # 112, Wednesday Afternoon