Down regulation of the expression of the p110, p85 and p55 subunits of phosphatidylinositol 3-kinase during colon cancer cell anchorage-independent growth.
We have found that analogues of phosphatidylinositol modified at the 3'-myo-inositol position prevent phosphorylation by phosphatidylinositol 3-kinase ( PI3-kinase) inhibit the anchorage-independent growth of HT-29 human colon adenocarcinoma cells as colonies in soft agarose but have no effect on monolayer growth on a plastic surface. Examination of an incomplete differential display library revealed 3 genes whose expression was increased and 11 genes whose expression was decreased or absent in HT-29 cells growing as colonies compared to monolayer growth. One of the cDNAs corresponding to an mRNA that was expressed only in cells growing as a monolayer was a 126 bp fragment that had 98% identity with a fragment of mRNA for human p55PIK PI3-kinase regulatory subunit. The down regulation of p55PIK gene expression in HT-29 cells growing as colonies was confirmed by RT-PCR using p55PIK-specific oligonucleotide primers. RT-PCR and Northern hybridisation were used to show that the expression of the p110 catalytic subunit and the p85 regulatory subunit of PI3-kinase were also down regulated in HT-29 cells growing as colonies. We measured a decrease of approximately 25% in total PI3-kinase activity of the HT-29 cells grown in soft agarose compared to HT-29 cells grown as monolayer. The results suggest that p110 PI3-kinase activity may be limiting in cells showing anchorage independent-growth which could explain their increased sensitivity, compared to cells in monolayer culture, to inhibitors of PI3-kinase signalling.[1]References
- Down regulation of the expression of the p110, p85 and p55 subunits of phosphatidylinositol 3-kinase during colon cancer cell anchorage-independent growth. Yeates, L.C., Gallegos, A., Kozikowski, A.P., Powis, G. Anticancer Res. (1999) [Pubmed]
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