pABC11 (also known as MOAT-C and MRP5), a member of the ABC family of proteins, has anion transporter activity but does not confer multidrug resistance when overexpressed in human embryonic kidney 293 cells

Several members of the ABC family of proteins have been implicated in multidrug resistance associated with cancer therapies. A novel member of this gene family, designated pABC11, has been identified using degenerate polymerase chain reaction. The full-length cDNA spans 5881 base pairs and encodes an open reading frame of 1437 amino acids predicted to contain two sets of transmembrane domains and two nucleotide binding domains characteristic of ABC proteins. The nucleotide sequence described herein extends that of three recently reported sequences, MRP5 (Kool, M., de Haas, M., Scheffer, G., Scheper, R., van Eijk, M., Juijn, J., Baas, F., and Borst, P. (1997) Cancer Res. 57, 3537-3547), SMRP (Suzuki, T., Nishio, K., Sasaki, H., Kurokawa, H., Saito-Ohara, F., Ikeuchi, T., Tanabe, S., Terada, M., and Saijo, N. (1997) Biochem. Biophys. Res. Commun. 238, 790-794), and MOAT-C (Belinsky, M., Bain, L., Balsara, B., Testa, J., and Kruh, G. (1998) J. Natl. Cancer Inst. 90, 1735-1741), in the 5' direction. Northern blot analysis detected five transcripts that were differentially expressed in several tissue types, and the gene encoding pABC11 was mapped to chromosome 3. Confocal imaging of HEK293 cells expressing a green fluorescent protein-pABC11 construct confirmed plasma membrane localization of the fusion protein. Overexpression of pABC11 resulted in reduced labeling with the fluorochromes 5-chloromethylfluorescein diacetate, fluorescein diacetate, and 2',7'-bis-(2-carboxyethyl)-5 (and-6)-carboxyfluorescein acetoxymethyl ester but not with calcein or rhodamine derivatives, consistent with pABC11 being an anion transporter. Fluorochrome export was ATP-dependent but glutathione-independent. We also show that this export pump does not confer resistance to various classes of cytotoxic drugs but does provide small but significant resistance to CdCl(2) and potassium antimonyl tartrate.

Human islets of Langerhans express multiple isoforms of calcium/calmodulin-dependent protein kinase II

Previous studies have provided evidence for the presence of calcium/calmodulin-dependent protein kinase II (CaM kinase II) in rodent islets of Langerhans, and beta-cell CaM kinase II activity has been correlated with insulin secretion. In this study we provide the first conclusive evidence for the expression of CaM kinase II in human islets of Langerhans and show that multiple isoforms are expressed. Screening of a human islet cDNA library resulted in the isolation of a 999bp partial cDNA clone encoding CaM kinase II. The nucleotide sequence of the islet clone showed a high degree of homology (94.8%) to the two gamma isoforms of CaM kinase II previously isolated from human T lymphocytes (gammaB and gammaC). In order to obtain full length sequence for the islet clone, rapid amplification of cDNA ends (RACE) was used to amplify the 3' end of the islet clone from human islet poly A+ RNA. Two distinct gamma isoforms of CaM kinase II were amplified from the islet RNA. They were identified as gammaB and gammaE; the latter is distinguished from gammaB by a 114bp insertion within the association domain of the cDNA. Using reverse transcriptase polymerase chain reaction (RT-PCR) we also detected in human islets of Langerhans the novel beta3 isoform of CaM kinase II previously reported to be expressed in neonatal rat islets.

A truncated isoform of Ca2+/calmodulin-dependent protein kinase II expressed in human islets of Langerhans may result from trans-splicing

Calcium/calmodulin-dependent protein kinase II (CaM kinase II) has been proposed to play a key role in glucose stimulated insulin secretion. Using the rapid amplification of cDNA ends technique we amplified the 3' end of the CaM kinase II gamma gene from human islet RNA. A novel cDNA was detected composed of 5' sequence from the human CaM kinase II gamma gene joined to the 3' end of the human signal recognition particle 72 (SRP72) gene. We predict that this mRNA species will code for a truncated form of CaM kinase II, designated gammaSRP, comprising the entire catalytic and regulatory domains of the protein and with a predicted molecular weight of 37 kDa. We mapped the human SRP72 gene to chromosome 18 and, as the CaM kinase II gamma gene was previously mapped to human chromosome 10q22, we suggest this novel cDNA may have resulted from trans-splicing.

Comparative biodisposition and metabolism of 14C-(+/-)-fenfluramine in mouse, rat, dog and man

1. The comparative metabolism of fenfluramine was investigated in mouse, rat, dog and man following a single oral dose of 14C-(+/-)-fenfluramine hydrochloride (1 mg/kg), and also in rat after eight consecutive 12-h subcutaneous doses (24 mg/kg). 2. Main route of excretion of radioactivity in all species and at all doses was into urine (> 80%), with only minor amounts of radioactivity found in faeces. 3. From all species examined a total of 11 metabolites were observed in urine and plasma by t.l.c. and h.p.l.c. analysis and no metabolite was present in the plasma which was not present in urine. 4. All species dealkylate fenfluramine to the active metabolite norfenfluramine, to a relative greater or lesser extent, with plasma metabolic ratios (norfenfluramine/fenfluramine) showing inter-animal variation (rat >> dog >> mouse = man). 5. These differences are due to the efficient deamination of both compounds to polar inactive metabolites in man, with less dealkylation and lower plasma levels of norfenfluramine compared with the other species studied. 6. In conclusion, major species differences in the metabolism of (+/-)-fenfluramine, both qualitative and quantitative were observed, and no one species had a similar metabolic profile to that found in man.