The 67-kDa laminin receptor (67LR) is a laminin-binding protein overexpressed in various types of cancer, including bile duct carcinoma, colorectal carcinoma, cervical cancer, and breast carcinoma. 67LR plays a vital role in growth and metastasis of tumor cells and resistance to chemotherapy. Here, we show that 67LR functions as a cancer-specific death receptor. In this cell death receptor pathway, cGMP initiated cancer-specific cell death by activating the PKCδ/acid sphingomyelinase (PKCδ/ASM) pathway. Furthermore, upregulation of cGMP was a rate-determining process of 67LR-dependent cell death induced by the green tea polyphenol (-)-epigallocatechin-3-O-gallate (EGCG), a natural ligand of 67LR. We found that phosphodiesterase 5 (PDE5), a negative regulator of cGMP, was abnormally expressed in multiple cancers and attenuated 67LR-mediated cell death. Vardenafil, a PDE5 inhibitor that is used to treat erectile dysfunction, significantly potentiated the EGCG-activated 67LR-dependent apoptosis without affecting normal cells and prolonged the survival time in a mouse xenograft model. These results suggest that PDE5 inhibitors could be used to elevate cGMP levels to induce 67LR-mediated, cancer-specific cell death.

EGCG [(−)-epigallocatechin-3-O-gallate], the major polyphenol of green tea, has cancer chemopreventive and chemotherapeutic activities. EGCG selectively inhibits cell growth and induces apoptosis in cancer cells without adversely affecting normal cells; however, the underlying molecular mechanism in vivo is unclear. In the present study, we show that EGCG-induced apoptotic activity is attributed to a lipid-raft clustering mediated through 67LR (67 kDa laminin receptor) that is significantly elevated in MM (multiple myeloma) cells relative to normal peripheral blood mononuclear cells, and that aSMase (acid sphingomyelinase) is critical for the lipid-raft clustering and the apoptotic cell death induced by EGCG. We also found that EGCG induces aSMase translocation to the plasma membrane and PKCδ (protein kinase Cδ) phosphorylation at Ser664, which was necessary for aSMase/ceramide signalling via 67LR. Additionally, orally administered EGCG activated PKCδ and aSMase in a murine MM xenograft model. These results elucidate a novel cell-death pathway triggered by EGCG for the specific killing of MM cells.

The bphC gene encoding 2,3-dihydroxybiphenyl dioxygenase was cloned from biphenyl-degrading and chlorinated biphenyl-degrading Pseudomonas paucimobilis Q1, and its complete nucleotide sequence was determined. The DNA-derived protein sequence provides the primary structure of 298 amino acids. Polyclonal antibodies raised against this protein from P. paucimobilis Q1 failed to cross-react with the previously isolated 2,3-dihydroxybiphenyl dioxygenase from Pseudomonas pseudoalcaligenes KF707 [Furukawa, K., & Arimura, N. (1987) J. Bacteriol. 169, 924-927. Furukawa, K., Arimura, N., & Miyazaki, T. (1987) J. Bacteriol. 169, 427-429], despite the close similarities of these proteins in terms of their native as well as subunit molecular weights, cofactor, and enzymatic activities. The sequence homology of the 2,3-dihydroxybiphenyl dioxygenase from the two different sources is examined.

No abstract

MicroRNAs (miRNAs) are non-coding RNAs involved in various biological processes by regulating their target genes. Green tea polyphenol (−)-epigallocatechin-3-O-gallate (EGCG) inhibits melanoma tumor growth by activating 67-kDa laminin receptor (67LR) signaling. To examine the effect of EGCG on miRNA expression in melanoma cells, we performed miRNA microarray analysis. We showed that EGCG up-regulated miRNA-let-7b expression through 67LR in melanoma cells. The EGCG-induced up-regulation of let-7b led to down-regulation of high mobility group A2 (HMGA2), a target gene related to tumor progression. 67LR-dependent cAMP/protein kinase A (PKA)/protein phosphatase 2A (PP2A) signaling pathway activation was involved in the up-regulation of let-7b expression induced by EGCG. These findings provide a basis for understanding the mechanism of miRNA regulation by EGCG.