Negative regulation of thyroid adenoma-associated protein (THADA) in the cardiac glycoside-induced anti-cancer effect.

Cardiac glycosides, known as inhibitors of Na+,K+-ATPase, have anti-cancer effects such as suppression of cancer cell proliferation and induction of cancer cell death. Here, we examined the signaling pathway elicited by cardiac glycosides in the human hepatocellular carcinoma HepG2 cells and human epidermoid carcinoma KB cells. Three kinds of cardiac glycosides (ouabain, oleandrin, and digoxin) inhibited the cancer cell proliferation and decreased the expression level of thyroid adenoma-associated protein (THADA). Interestingly, the knockdown of THADA inhibited cancer cell proliferation, and the proliferation was significantly rescued by re-expression of THADA in the THADA-knockdown cells. In addition, the THADA-knockdown markedly decreased the expression level of L-type amino acid transporter LAT1. Cardiac glycosides also reduced the LAT1 expression. The LAT1 inhibitor, JPH203, significantly weakened the cancer cell proliferation. These results suggest that the binding of cardiac glycosides to Na+,K+-ATPase negatively regulates the THADA-LAT1 pathway, exerting the anti-proliferative effect in cancer cells.

Clinical utility of urinary mulberry bodies/cells testing in the diagnosis of Fabry disease.

Introduction: Variants in the galactosidase alpha (GLA) gene cause Fabry disease (FD), an X-linked lysosomal storage disorder caused by α-galactosidase A (α-GAL) deficiency. Recently, disease-modifying therapies have been developed, and simple diagnostic biomarkers for FD are required to initiate these therapies in the early stages of the disease. Detection of urinary mulberry bodies and cells (MBs/MCs) is beneficial for diagnosing FD. However, few studies have evaluated the diagnostic accuracy of urinary MBs/MCs in FD. Herein, we retrospectively evaluated the diagnostic ability of urinary MBs/MCs for FD. Methods: We analyzed the medical records of 189 consecutive patients (125 males and 64 females) who underwent MBs/MCs testing. Out of these, two female patients had already been diagnosed with FD at the time of testing, and the remaining 187 patients were suspected of having FD and underwent both GLA gene sequencing and/or α-GalA enzymatic testing. Results: Genetic testing did not confirm the diagnosis in 50 females (26.5%); hence, they were excluded from the evaluation. Two patients were previously diagnosed with FD, and sixteen were newly diagnosed. Among these 18 patients, 15, including two who had already developed HCM at diagnosis, remained undiagnosed until targeted genetic screening of at-risk family members of patients with FD was performed. The accuracy of urinary MBs/MCs testing exhibited a sensitivity of 0.944, specificity of 1, positive predictive value of 1, and negative predictive value of 0.992. Conclusions: MBs/MCs testing is highly accurate in diagnosing FD and should be considered during the initial evaluation prior to genetic testing, particularly in female patients.

Activation of mouse Otop3 proton channels by Zn2.

Otopetrins (Otop1-Otop3) belong to a newly identified family of proton (H+) channels activated by extracellular acidification. Here, we found that Zn2+ activates the mouse Otop3 (mOtop3) proton channels by using electrophysiological patch-clamp techniques. In mOtop3-expressing human embryonic kidney HEK293T cells, a biphasic inward mOtop3 H+ current comprising a fast transient current followed by a sustained current was observed upon extracellular acidification at pH 5.0. No significant activation of the mOtop3 channel was observed at pH 6.5 and 7.4, but interestingly, Zn2+ dose-dependently induced a sustained activation of mOtop3 under these pH conditions. Increasing the Zn2+ concentration had no effect on the reversal potential of the channel currents, suggesting that Zn2+ does not permeate through the mOtop3. The activation of the mOtop3 channel was specific to Zn2+ among divalent metal cations. Our findings reveal a novel modulatory mechanism of mOtop3 proton channels by Zn2+.

Cardiac glycosides stimulate endocytosis of GLUT1 via intracellular Na+ ,K+ -ATPase α3-isoform in human cancer cells.

Glucose transporter GLUT1 plays a primary role in the glucose metabolism of cancer cells. Here, we found that cardiac glycosides (CGs) such as ouabain, oleandrin, and digoxin, which are Na+ ,K+ -ATPase inhibitors, decreased the GLUT1 expression in the plasma membrane of human cancer cells (liver cancer HepG2, colon cancer HT-29, gastric cancer MKN45, and oral cancer KB cells). The effective concentration of ouabain was lower than that for inhibiting the activity of Na+ ,K+ -ATPase α1-isoform (α1NaK) in the plasma membrane. The CGs also inhibited [3 H]2-deoxy- d-glucose uptake, lactate secretion, and proliferation of the cancer cells. In intracellular vesicles of human cancer cells, Na+ ,K+ -ATPase α3-isoform (α3NaK) is abnormally expressed. Here, a low concentration of ouabain inhibited the activity of α3NaK. Knockdown of α3NaK significantly inhibited the ouabain-decreased GLUT1 expression in HepG2 cells, while the α1NaK knockdown did not. Consistent with the results in human cancer cells, CGs had no effect on GLUT1 expression in rat liver cancer dRLh-84 cells where α3NaK was not endogenously expressed. Interestingly, CGs decreased GLUT expression in the dRLh-84 cells exogenously expressing α3NaK. In HepG2 cells, α3NaK was found to be colocalized with TPC1, a Ca2+ -releasing channel activated by nicotinic acid adenine dinucleotide phosphate (NAADP). The CGs-decreased GLUT1 expression was significantly inhibited by a Ca2+ chelator, a Ca2+ -ATPase inhibitor, and a NAADP antagonist. The GLUT1 decrease was also attenuated by inhibitors of dynamin and phosphatidylinositol-3 kinases (PI3Ks). In conclusion, the binding of CGs to intracellular α3NaK elicits the NAADP-mediated Ca2+ mobilization followed by the dynamin-dependent GLUT1 endocytosis in human cancer cells.

Survival of detached cancer cells is regulated by movement of intracellular Na+,K+-ATPase.

Beginning of metastasis, cancer cells detach from the primary tumor and they can survive even under loss of anchorage; however, the detachment-elicited mechanisms have remained unknown. Here, we found that Na+,K+-ATPase α3-isoform (α3NaK) in human cancer cells is dynamically translocated from intracellular vesicles to the plasma membrane when the attached cells are detached and that this mechanism contributes to the survival of the detached (floating) cancer cells. α3NaK was detected in the plasma membrane of floating cancer cells in peritoneal fluids of patients, while it was in the cytoplasm of the cells in primary tumor tissues. On cancer cell detachment, we also found the focal-adhesion-kinase-dependent Ca2+ response that induces the α3NaK translocation via nicotinic acid adenine dinucleotide phosphate pathway. Activation of AMP-activated protein kinase was associated with the translocated α3NaK in the plasma membrane. Collectively, our study identifies a unique mechanism for survival of detached cancer cells, opening up new opportunities for development of cancer medicines.