Lack of immunological cross reactivity between the transport enzymes (Na+ + K+)-ATPase and (K+ + H+)-ATPase

Human Lung Mucous Glands Manifest Evidence of the H+/K+-ATPase Proton Pump

Objectives:

The H+/K+-ATPase proton pump has been demonstrated in human laryngeal submucosal glands, and is not solely present in the parietal cells of the stomach. Although proton secretion is present in the lung, a variety of mechanisms have been elucidated. The hypothesis of this study is that the H+/K+-ATPase proton pump is one additional pathway of proton secretion in the human lung.

Methods:

Fourteen surgical lung specimens from 10 subjects were retrospectively obtained after approval from our Human Subjects Committee. Banked human stomach tissue was used for comparative positive and negative controls. Sections were immunostained with 2 monoclonal antibodies selectively reactive with alpha or beta subunits of the H+/K+-ATPase proton pump.

Results:

In the human lung, consistent staining for both subunits was present in the mucous gland cells and ducts in all specimens in which mucous glands were present (6 specimens from 5 subjects). Overall, weak to strong staining was present in focal areas within the multicellular mucous glands. There was only scant focal staining in the respiratory epithelium in 4 specimens. Stomach parietal cells exhibited strongly positive staining for both subunits of the proton pump. There was no staining in stomach cells that were not morphologically consistent with parietal cells.

Conclusions:

The H+/K+-ATPase proton pump is present in mucous cells and ducts in the human lung, with some variable expression noted. Proton pump inhibitor pharmacotherapy may have a site of action in the human lung, explaining some of the controversies otherwise attributable to interrelatedness of aerodigestive tract disease.

The H+/K+-ATPase (proton) pump is expressed in human laryngeal submucosal glands

OBJECTIVES/HYPOTHESIS

Diagnosis and treatment of gastroesophageal and laryngopharyngeal reflux disease has significantly increased over recent years. The larynx is highly sensitive to the effects of LPRD and is similarly responsive to proton pump inhibitor pharmacotherapy. The hypothesis of the study was that proton pump activity exists in the human larynx and plays a functional role in normal and/or pathological laryngeal tissue.

STUDY DESIGN

Pathological investigation.

METHODS

Two fresh human cadaveric larynges (one male and one female larynx) were obtained as part of an exempt protocol from the Human Subjects Committee and were formalin fixed and paraffin embedded. Banked human stomach tissue was also obtained for use as comparative positive and negative control specimens. Sections were immunostained with monoclonal antibodies reactive with both alpha and beta subunits of the H+/K+-ATPase (proton) pump. Specimens were reviewed for staining pattern and intensity.

RESULTS

Stomach parietal cells (known to produce gastric acid) exhibited strongly positive staining for both the alpha and beta subunits of the proton pump. There was no staining in stomach cells that were not morphologically consistent with the parietal cell. In the human larynx there were strong focal and identical staining patterns in the serous cells and ducts of the minor seromucinous glands by both alpha and beta monoclonals to the proton pump. There was variable staining in the laryngeal epithelium that was thought to be consistent with artifact staining resulting from tissue processing.

CONCLUSION

The H+/K+-ATPase (proton) pump is present in serous cells and ducts of submucosal glands in the human larynx. Proton pump inhibitor pharmacotherapy may have a site of action in seromucinous glands of the human larynx, with possible relevance for patients treated for chronic laryngitis with or without laryngopharyngeal reflux disease.

Proton pump (H+/K+-ATPase) expression in human laryngeal seromucinous glands

OBJECTIVE

Recent pilot research suggested that the H+/K+-ATPase (proton pump), which is the target of pharmacotherapy for laryngopharyngeal reflux disease (LPRD), is associated with human laryngeal submucosal glands. The hypothesis of this study is that proton pump is expressed in the human larynx, and is not solely associated with the parietal cells of the stomach.

METHODS

Fifteen surgical larynx subjects (27 pathologic specimens) containing seromucinous glands from banked tissue were retrospectively obtained after approval from Human Subjects Committee. Banked human stomach tissue was also obtained for comparative positive and negative controls. Sections were immunostained with two monoclonal antibodies selectively reactive with alpha or beta subunits of the H+/K+-ATPase (proton) pump.

RESULTS

In the human larynx, positive staining was seen in 14 of 15 subjects. Twenty-six specimens showed consistent staining in the seromucinous cells and ducts for the alpha subunit, and 23 specimens for the beta subunit. Stomach parietal cells exhibited strongly positive staining for both the alpha and beta subunits of the proton pump. There was no staining in stomach cells that were not morphologically consistent with the parietal cell.

CONCLUSION

The H+/K+-ATPase (proton) pump is present in seromucinous cells and ducts in the human larynx, with some variable expression noted. Proton pump involvement in human laryngeal seromucinous glands may explain heightened laryngeal sensitivity in those patients with chronic laryngitis believed to have LPRD. Also, proton pump inhibitor pharmacotherapy may have a site of action in the human larynx, explaining some of the controversies attributable to LPRD.

EBM RATING

B-3.

The MRP4/ABCC4 gene encodes a novel apical organic anion transporter in human kidney proximal tubules: putative efflux pump for urinary cAMP and cGMP

The cyclic nucleotides cAMP and cGMP play key roles in cellular signaling and the extracellular regulation of fluid balance. In the kidney, cAMP is excreted across the apical proximal tubular membrane into urine, where it reduces phosphate reabsorption through a dipyridamole-sensitive mechanism that is not fully understood. It has long been known that this cAMP efflux pathway is dependent on ATP and is inhibited by probenecid. However, its identity and whether cGMP shares the same transporter have not been established. Here the expression, localization, and functional properties of human multidrug resistance protein 4 (MRP4) are reported. MRP4 is localized to the proximal tubule apical membrane of human kidney, and membrane vesicles from Sf9 cells expressing human MRP4 exhibit ATP-dependent transport of [(3)H]cAMP and [(3)H]cGMP. Both probenecid and dipyridamole are potent MRP4 inhibitors. ATP-dependent [(3)H]methotrexate and [(3)H]estradiol-17beta-D-glucuronide transport by MRP4 and interactions with the anionic conjugates S-(2,4-dinitrophenyl)-glutathione, N-acetyl-(2,4-dinitrophenyl)-cysteine, alpha-naphthyl-beta-D-glucuronide, and p-nitrophenyl-beta-D-glucuronide are also demonstrated. In kidneys of rats deficient in the apical anionic conjugate efflux pump Mrp2, Mrp4 expression is maintained at the same level. It is concluded that MRP4 is a novel apical organic anion transporter and the putative efflux pump for cAMP and cGMP in human kidney proximal tubules.

Chimeras of X+, K+-ATPases. The M1-M6 region of Na+, K+-ATPase is required for Na+-activated ATPase activity, whereas the M7-M10 region of H+, K+-ATPase is involved in K+ de-occlusion

In this study we reveal regions of Na(+),K(+)-ATPase and H(+),K(+)-ATPase that are involved in cation selectivity. A chimeric enzyme in which transmembrane hairpin M5-M6 of H(+),K(+)-ATPase was replaced by that of Na(+),K(+)-ATPase was phosphorylated in the absence of Na(+) and showed no K(+)-dependent reactions. Next, the part originating from Na(+),K(+)-ATPase was gradually increased in the N-terminal direction. We demonstrate that chimera HN16, containing the transmembrane segments one to six and intermediate loops of Na(+),K(+)-ATPase, harbors the amino acids responsible for Na(+) specificity. Compared with Na(+),K(+)-ATPase, this chimera displayed a similar apparent Na(+) affinity, a lower apparent K(+) affinity, a higher apparent ATP affinity, and a lower apparent vanadate affinity in the ATPase reaction. This indicates that the E(2)K form of this chimera is less stable than that of Na(+),K(+)-ATPase, suggesting that it, like H(+),K(+)-ATPase, de-occludes K(+) ions very rapidly. Comparison of the structures of these chimeras with those of the parent enzymes suggests that the C-terminal 187 amino acids and the beta-subunit are involved in K(+) occlusion. Accordingly, chimera HN16 is not only a chimeric enzyme in structure, but also in function. On one hand it possesses the Na(+)-stimulated ATPase reaction of Na(+),K(+)-ATPase, while on the other hand it has the K(+) occlusion properties of H(+),K(+)-ATPase.

Regulation of expression of Na+,K+-ATPase in androgen-dependent and androgen-independent prostate cancer

The beta 1-subunit of Na+,K+-ATPase was isolated and identified as an androgen down-regulated gene. Expression was observed at high levels in androgen-independent as compared to androgen-dependent (responsive) human prostate cancer cell lines and xenografts when grown in the presence of androgens. Down-regulation of the beta 1-subunit was initiated at concentrations between 0.01 nM and 0.03 nM of the synthetic androgen R1881 after relatively long incubation times (> 24 h). Using polyclonal antibodies, the concentration of beta 1-subunit protein, but not of the alpha 1-subunit protein, was markedly reduced in androgen-dependent human prostate cancer cells (LNCaP-FGC) cultured in the presence of androgens. In line with these observations it was found that the protein expression of total Na+,K+-ATPase in the membrane (measured by 3H-ouabain binding) was also markedly decreased. The main function of Na+,K+-ATPase is to maintain sodium and potassium homeostasis in animal cells. The resulting electrochemical gradient is facilitative for transport of several compounds over the cell membrane (for example cisplatin, a chemotherapeutic agent experimentally used in the treatment of hormone-refractory prostate cancer). Here we observed that a ouabain-induced decrease of Na+,K+-ATPase activity in LNCaP-FGC cells results in reduced sensitivity of these cells to cisplatin-treatment. Surprisingly, androgen-induced decrease of Na+,K+-ATPase expression, did not result in significant protection against the chemotherapeutic agent.

A monoclonal antibody against pig gastric H+/K(+)-ATPase, which binds to the cytosolic E1.K+ form

Monoclonal antibodies were raised against a purified membrane fraction from hog gastric mucosa containing H+/K(+)-ATPase. The properties of one of these monoclonal antibodies (5B6) were further evaluated. On immunoblot it recognized the 95 kDa peptide of the H+/K(+)-ATPase-rich membrane fraction. The K(+)-ATPase activity was inhibited by 65% under standard assay conditions (pH 7.0). At pH 6.0 and 8.0 this enzyme activity was inhibited by 40% and 100%, respectively. The maximal inhibition in inside-out vesicles was also 65% at pH 7.0. The inhibition was uncompetitive with respect to K+ and noncompetitive with respect to ATP. Mg2(+)-ATPase activity and K(+)-dependent p-nitrophenylphosphatase activity were not influenced. The monoclonal antibody lowered the steady-state phosphorylation level at pH 6.0, 7.0 and 8.0 by 30%, 40% and 60% respectively. The rate of the K(+)-stimulated dephosphorylation step was not inhibited. These findings demonstrate that 5-B6 recognizes the E1.K+ dephosphoenzyme at the cytosolic side.

Structural studies on H+,K+-ATPase: determination of the NH2-terminal amino acid sequence and immunological cross-reactivity with Na+,K+-ATPase

The NH2-terminal amino acid sequence of the 100 kilodalton subunit of porcine gastric H+,K+-ATPase has been determined to be YKAENYELYQVELGPGP. Although the NH2-terminal region of this protein is not similar to the same region of the lamb kidney Na+,K+-ATPase catalytic subunit, other regions of these ATPase proteins appear to be homologous. Both monoclonal and polyclonal antibodies raised to lamb kidney Na+,K+-ATPase and its alpha, but not beta, subunit cross-react with the 100 kilodalton protein of H+,K+-ATPase.