Caloxins: a novel class of selective plasma membrane Ca2+ pump inhibitors obtained using biotechnology

Abstract

Plasma membrane Ca2+ pumps (PMCA) extrude cellular Ca2+ with a high affinity and hence play a major role in Ca2+ homeostasis and signaling. Caloxins (selective extracellular PMCA inhibitors) would aid in elucidating the physiology of PMCA. PMCA proteins have five extracellular domains (exdoms). Our hypotheses are: 1) peptides that bind selectively to each exdom can be invented by screening a random peptide library, and 2) a peptide can modulate PMCA activity by binding to one of the exdoms. The first caloxin 2a1, selected for binding exdom 2 was selective for PMCA (Ki=529 microM). It has been used to examine the physiological role of PMCA. PMCA isoforms are encoded by four genes. PMCA isoform expression differs in various cell types, with PMCA1 and 4 being the most widely distributed. There are differences between PMCA1-4 exdom 1 sequences, which may be exploited for inventing isoform selective caloxins. Using exdom 1 of PMCA4 as a target, modified screening procedures and mutagenesis led to the high-affinity caloxin 1c2 (Ki=2.3 microM for PMCA4). It is selective for PMCA4 over PMCA1, 2, or 3. We hope that caloxins can be used to discern the roles of individual PMCA isoforms in Ca2+ homeostasis and signaling. Caloxins may also become clinically useful in cardiovascular diseases, neurological disorders, retinopathy, cancer, and contraception.

A diversity of SERCA Ca2+ pump inhibitors

“…In addition to causing autophagy and cell death in a number of cancer cell lines, this compound was also shown to elevate intracellular Ca 2+ levels via SERCA inhibition (IC 50 27 μM) [15]. The structure of Alisol B is steroid in nature with a ketone group at the C-3 position and a branched acyl hydroxylated epoxide side chain at the C-17 position ( Figure 1) [15].…”

Human Th1 and Th2 lymphocytes are distinguished by calcium flux regulation during the first 10min of lymphocyte activation

“…The applied concentrations of the inhibitors were set based on literary data (Chaudhary et al, 2001;Hajnóczky et al, 2006;Matlib et al, 1998;Szewczyk et al, 2008;Thastrup et al, 1990;Xu et al, 1999) and on preliminary control measurements regarding inhibitory efficacy.…”

“…We investigated the contribution of the ER calcium release, the CRAC channel, and, using specific inhibitors, the MCU (inhibited by ruthenium red (RR) (Hajnóczky et al, 2006;Matlib et al, 1998;Xu et al, 1999)), the SERCA pump (inhibited by thapsigargin (TG) (Thastrup et al, 1990)) and the PMCA pump (inhibited by caloxin 2A1 (Chaudhary et al, 2001;Szewczyk et al, 2008)) to the regulation of [Ca 2+ ] cyt during the early period (first 10 min) of T lymphocyte activation and found significant differences between these subsets.…”

Plasma membrane calcium ATPases (PMCAs) as potential targets for the treatment of essential hypertension

“…The availability of the PMCA4 knockout mouse affords the opportunity for investigation of the effects of PMCA4 ablation on BP and arterial contractility. For any clear consensus on the role of PMCA4 in vascular contractility, assessment of a different class of PMCA4 inhibitors, with increased specificity, needs to be made (Pande et al, 2006Szewczyk et al, 2008). Indeed, the recent identification of ATA as a highly selective PMCA4 inhibitor (Mohamed et al, 2013) has advanced the pharmacology in this field, and may prove to be a highly useful tool in defining the contribution of PMAC4 to BP regulation.…”