Aggressive cancers such as glioblastoma (GBM) contain intermingled apoptotic cells adjacent to proliferating tumor cells. Nonetheless, intercellular signaling between apoptotic and surviving cancer cells remain elusive. In this study, we demonstrate that apoptotic GBM cells paradoxically promote proliferation and therapy resistance of surviving tumor cells by secreting apoptotic extracellular vesicles (apoEVs) enriched with various components of spliceosomes. apoEVs alter RNA splicing in recipient cells, thereby promoting their therapy resistance and aggressive migratory phenotype. Mechanistically, we identified RBM11 as a representative splicing factor that is upregulated in tumors after therapy and shed in extracellular vesicles upon induction of apoptosis. Once internalized in recipient cells, exogenous RBM11 switches splicing of MDM4 and Cyclin D1 toward the expression of more oncogenic isoforms.

Although the functional role of nicotinamide nucleotide transhydrogenase (Nnt) remains to be fully elucidated, there is strong evidence that Nnt plays a critical part in mitochondrial metabolism by maintaining a high NADPH-dependent GSH/GSSG ratio, and thus the control of cellular oxidative stress. Using real-time PCR, spectrophotometric and western blotting techniques, we sought to determine the presence, abundance and activity level of Nnt in human heart tissues and to discern whether these are altered in chronic severe heart failure. Left ventricular levels of the NNT gene and protein expression did not differ significantly between the non-failing donor (NF) and heart failure (HF) group. Notably, compared to NF, Nnt activity rates in the HF group were 18% lower, which coincided with significantly higher levels of oxidized glutathione, lower glutathione reductase activity, lower NADPH and a lower GSH/GSSG ratio. In the failing human heart a partial loss of Nnt activity adversely impacts NADPH-dependent enzymes and the capacity to maintain membrane potential, thus contributing to a decline in bioenergetic capacity, redox regulation and antioxidant defense, exacerbating oxidative damage to cellular proteins.

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We have identified the fifth member of the mammalian X,K-ATPase L L-subunit gene family. The human and rat genes are largely expressed in skeletal muscle and at a lower level in heart. The deduced human and rat proteins designated as L L muscle (L L m ) consist of 357 and 356 amino acid residues, respectively, and exhibit 89% identity. The sequence homology of L L m proteins with known Na,K-and H,K-ATPase L L-subunits are 30.5^39.4%. Unlike other L L-subunits, putative L L m proteins have large N-terminal cytoplasmic domains containing long Glurich sequences. The data obtained indicate the existence of hitherto unknown X,K-ATPase (most probably Na,K-ATPase) isozymes in muscle cells.z 1999 Federation of European Biochemical Societies.

Human ATP1AL1 and corresponding genes of other mammals encode the catalytic K

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The molecular basis of active ion transport in secretory glands such as the prostate is not well characterized. Rat nongastric H-K-ATPase is expressed at high levels in distal colon surface cell apical membranes and thus is referred to as “colonic.” Here we show that the ATPase is expressed in rodent prostate complex in a lobe-specific manner. RT-PCR and Western blot analyses indicate that rat nongastric H-K-ATPase α-subunit (αng) mRNA and protein are present in coagulating gland (anterior prostate) and lateral and dorsal prostate and absent from ventral lobe, whereas Na-K-ATPase α-subunit is present in all lobes. RT-PCR analysis shows that Na-K-ATPase α4 and α3 and gastric H-K-ATPase α-subunit are not present in significant amounts in all prostate lobes. Relatively low levels of Na-K-ATPase α2were found in lateral, dorsal, and anterior lobes. αngprotein expression is anteriodorsolateral: highest in coagulating gland, somewhat lower in dorsal lobe, and even lower in lateral lobe. Na-K-ATPase protein abundance has the reverse order: expression in ventral lobe is higher than in coagulating gland. αngprotein abundance is higher in coagulating gland than distal colon membranes. Immunohistochemistry shows that in rat and mouse coagulating gland epithelium αng protein has an apical polarization and Na-K-ATPase α1 is localized in basolateral membranes. The presence of nongastric H-K-ATPase in rodent prostate apical membranes may indicate its involvement in potassium concentration regulation in secretions of these glands.

Change in gene functions (gene cooption) is one of the key mechanisms of molecular evolution. Genes can acquire new functions via alteration in properties of encoded proteins and/or via changes in temporal or spatial regulation of expression. Here we demonstrate radical changes in the functions of orthologous ATP1B4 genes during evolution of vertebrates. Expression of ATP1B4 genes is brain-specific in teleost fishes, whereas it is predominantly muscle-specific in tetrapods. The encoded ␤m-proteins in fish, amphibian, and avian species are ␤-subunits of Na,K-ATPase located in the plasma membrane. In placental mammals ␤m-proteins lost their ancestral functions, accumulate in nuclear membrane of perinatal myocytes, and associate with transcriptional coregulator Ski-interacting protein (SKIP). Through interaction with SKIP, eutherian ␤m acquired new functions as exemplified by regulation of TGF-␤-responsive reporters and by augmentation of mRNA levels of Smad7, an inhibitor of TGF-␤ signaling. Thus, orthologous vertebrate ATP1B4 genes represent an instance of gene cooption that created fundamental changes in the functional properties of the encoded proteins.ATP1B4 ͉ gene cooption ͉ skeletal muscle development ͉ TGF-␤ ͉ Smad7