Conserved Regulation of Cardiac Calcium Uptake by Peptides Encoded in Small Open Reading Frames

Abstract

Small open reading frames (smORFs) are short DNA sequences that are able to encode small peptides of less than 100 amino acids. Study of these elements has been neglected despite thousands existing in our genomes. We and others previously showed that peptides as short as 11 amino acids are translated and provide essential functions during insect development. Here, we describe two peptides of less than 30 amino acids regulating calcium transport, and hence influencing regular muscle contraction, in the Drosophila heart. These peptides seem conserved for more than 550 million years in a range of species from flies to humans, in which they have been implicated in cardiac pathologies. Such conservation suggests that the mechanisms for heart regulation are ancient and that smORFs may be a fundamental genome component that should be studied systematically.

Decoding sORF translation – from small proteins to gene regulation

“…19,[35][36][37][38][39][40][41][42] The majority of these newly identified short proteins show a higher degree of amino acid sequence conservation than observed in known regulatory translation events. The modes of action of these short proteins are divers and comprise intra-as well as extracellular functions (Fig.…”

“…74 Apart from signaling to other cells as secreted factors, it is also feasible that membrane-bound short proteins could act as (co-)receptors or as cell adhesion molecules. While specific examples for such functionalities have to our knowledge not yet been identified, the SERCA regulators PLN, SLN, MLN and DWORF 38,40,41 provide the proof-of-principle that functional, cell membrane-embedded short proteins exist.…”

“…SERCA is an ATPase located in the membrane of the sarcoplasmic reticulum (SR), where it pumps Ca 2C back into the SR after Ca 2C release upon muscle contraction. SERCA was recently shown to be inhibited by 3 short proteins, namely phospholamban (PLN/PLB), sacrolipin (SLN) and myoregulin (MLN), 38,40 while the short protein DWORF (dwarf open reading frame) enhances SERCA activity by displacing those inhibitory proteins. 41 Apart from allosteric regulation, it is also feasible that short proteins could negatively regulate enzyme activities by competing with enzymatic substrates for binding to the active site.…”

“…13,17,20,26,31,32 Apart from 'technical noise', there is 'biological noise' that originates from genuine translation, yet neither the peptide product nor the act of translation of this particular sequence might serve any specific purpose. Because there is ample evidence that at least some sORFs do have essential functions in vivo, 19,[33][34][35][36][37][38][39][40][41][42] we will omit further discussions of noise and focus on functional aspects of sORF translation.…”

The Persistent Contributions of RNA to Eukaryotic Gen(om)e Architecture and Cellular Function

“…If humans were not pentadactyls, but hexa-or tetradactyls, the cutoff would probably have been chosen at 144 or 64 amino acids, respectively. There are numerous mRNAs that have even shorter ORFs, namely, those encoding peptides (Rudd et al 1998;Sousa et al 2001;Frith et al 2006a;Kastenmayer et al 2006;Savard et al 2006;Galindo et al 2007;Ghabrial 2007;Hanada et al 2007;Hashimoto et al 2008;Magny et al 2013). Perhaps a significant fraction of mRNA-like long intervening non-protein-coding RNAs are mRNAs after all, encoding peptides and short proteins.…”