RESUMO
Mutations in the serine-threonine tumor-suppressor kinase LKB1 are responsible for Peutz-Jeghers syndrome, characterized by hamartomatous proliferation and an increased risk of developing cancer. Mutations in lkb1 have also been identified in sporadic cancers, suggesting a wider role for LKB1 in cancer that is not limited to hamartomatous polyposis syndromes. Here, we show that LKB1 catalytically deficient mutants, when introduced into DLD1p21-/-p53-/- colorectal cancer cells, allowed for progression of cells through to S phase of cell cycle and elicited the expression of Rb, cyclin E, and cyclin A2 whereas the introduction of LKB1 lead to G1 cell cycle arrest independent of p21(WAF/CIP1) and/or p53 expression. Furthermore, we show that LKB1 catalytically deficient mutants activate the expression of cyclin D1 through recruitment to response elements within the promoter of the oncogene. In addition to compromising the tumor-suppressor function of LKB1, our findings highlight an emerging role for LKB1 catalytically deficient mutants, a gain of oncogenic properties.
Assuntos
Adenocarcinoma/metabolismo , Transformação Celular Neoplásica/metabolismo , Neoplasias Colorretais/metabolismo , Ciclina D1/biossíntese , Proteínas Serina-Treonina Quinases/metabolismo , Quinases Proteína-Quinases Ativadas por AMP , Adenocarcinoma/genética , Western Blotting , Ciclo Celular/fisiologia , Proliferação de Células , Neoplasias Colorretais/genética , Inibidor de Quinase Dependente de Ciclina p21/deficiência , Citometria de Fluxo , Humanos , Imunoprecipitação , Mutação , Proteínas Serina-Treonina Quinases/genética , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Transfecção , Proteína Supressora de Tumor p53/deficiênciaRESUMO
In the present study, we compare changes in host cell plasma membrane potential (V(m)), K(+) fluxes, and NO production during K(+) channel blockade with those changes that occur during infection with Leishmania major. Infection of P388D.1 cells with L. major promastigotes or treatment with K(+) channel blockers (either 1mM 4-AP, 10mM TEA, or 200 microM quinine) suppressed NO production. Inhibition of NO production correlated with depolarization of the P388D.1 cell V(m). Infection of P388D.1 cells with L. major increased the unidirectional influx of rubidium (86Rb), a tracer for K(+) flux, that was comparable to that induced by K(+) channel blockade by 1mM 4-AP. The similar effects of K(+) channel blockers and L. major on NO production, K(+) influx, and V(m) suggest that K(+) channel activity and the maintenance of V(m) is important for NO production in these cells. We suggest that intracellular parasites employ a strategy to inhibit NO production by disrupting V(m) during the invasion/infection process by altering host cell K(+) channel activity.