G-protein γ 7 is down-regulated in cancers and associated with P 27(kip1)-induced growth arrest

We previously identified and cloned human G protein γ 7 (G-γ 7) gene, which is down-regulated in pancreatic cancer. We examined G-γ 7 expression in other gastrointestinal tract cancers. In 24 of 30 patients with gastrointestinal tract cancer, Northern blot assay and immunohistochemical staining revealed significantly lower G-γ 7 expression in tumors than in normal tissues from the same patients. Semiquantitative reverse transcription PCRs also showed lower G-γ 7 expression in tumors than in corresponding normal tissues in 69 of 90 patients. To examine the biological role of G-γ 7 in cancer, the G-γ 7 cDNA was transfected into a human esophageal carcinoma cell line, KYSE150, that lacks G-γ 7 expression. G-γ 7 expression suppressed cell growth and tritiated-thymidine uptake when cells were confluent. G-γ 7 expression also suppressed tumorigenicity in BALB/c nude mice until 3 weeks after transplantation. G-γ 7 expression increased the G₀/G₁ population and decreased the S phase population when cells were at high density. We confirmed that this change was associated with p27(Kip1) expression. These findings suggest that human G-γ 7 is associated with p27(kip1)-induced growth arrest and may be a therapeutic target in cancers.