## 1 Introduction  
Proprotein converses (PCs) comprise a family of nine secretory proteases related to bacterial subtilisin and yeast kexin (genes _PCSK1_ to _PCSK9_) [1]. PCs cleave their protein precursors at basic and non-basic amino acid sites. Seven out of nine PCs, namely PC1/3, PC2, Furin, PC4, PC5/6, PACE4, and PC7, belong to a subgroup that cleaves its substrates at either single or pairs of basic amino acids within the motif [R/K]-2(Xn)-[R/K]\({}_{\downarrow}\) (Xn stands for 0-3 spacer amino acids), while SKI-1/S1P and PCSK9 oleave their substrates and/or themselves at non-basic sites [1]. The _PCSK7_ gene, harbored on chromosome 11q23,3 encodes the most ancient and highly conserved type-I membrane-bound protease, termed \"PC7\", which is ubiquitously expressed [2]. The mature form of PC7, as is the case with all other PCs, is the result of a sequential two autocatalytic processing (cleavage) events. PC7 is initially synthesized as a proPC7 zymogen (\(\sim\)102 kDa) in the endoplasmic reticulum (ER), which is then autocatalytically cleaved in the ER to produce an inactive PC7 (\(\sim\)92 kDa) that is noncovalently bound to its N-terminal inhibitory prodomain [3; 4]. Further, posttranslational modifications of PC7 such as N-glycosylation, Tyr-sulfation, and Cys-palmitoylation of the cytosolic tail at residues Cys699 and Cys704 occur in the ER and _cis-medial_ -Golgi [2; 5; 6]. The prodomain-PC7 complex is then activated in endosomes and constantly transits between the _trans_-Golgi network and the cell surface [7; 8; 9; 10; 11]. The various mechanisms underlying PC7 activation and functions are still not well defined; nonetheless, it is now known that PC7 exerts its activity via enzymatic [8; 12] and non-enzymatic [13] mechanisms to regulate specific protein targets. As a protease, PC7 is specifically implicated in iron homeostasis by shedding human transferrin receptor 1 (hTfR1). To date, the shedding of hTfR1 is the only recognized specific substrate of PC7 cleaved at Arg100\(\downarrow\) within the sequence KTCECER\({}_{100\downarrow}\)LA [8]. PC7 is also implicated in the shedding of the cancer-associated proteins CASC4 and GPP130 [14]. We also demonstrated that PC7 enhances the processing of the cell surface pro-epidermal growth factor [15] and brain-derived neurotrophic factor (BDNF) [12]. In addition, triglyceride metabolism is modulated by PC7, in part owing to its ability to non-enzymatically regulate the levels of circulating apolipoprotein A-V [13], an activator of lipoprotein lipase, and possibly other secretory lipoproteins starting in the endoplasmic reticulum. This led to the suggestion that PC7 inhibition could be useful to treat metabolic dysfunction-associated fatty liver disease (MAFLD) and hepatic steatosis [16; 17], and possibly in iron regulation in hereditary haemochromatosis [18]. In fact, it has been suggested that PC7 could be a target for the treatment of dyslipidemia, e.g., triglyceride-associated fatty liver disease [19]. Accumulating research in recent years has demonstrated that microRNAs (miRNAs), which constitute a highly evolutionarily conserved class of small (18-22 nucleotides) non-coding RNAs, post-transcriptionally modulate gene expression by either repressing translation or promoting messenger RNA (mRNA) degradation via binding to the three prime untranslated regions (3'-UTRs) of their target mRNAs [20; 21; 22]. Acting as fine-tuners or micromanagers of gene expression of more than 60% of human protein-coding genes, these small-molecule regulators effectively control a wide spectrum of molecular pathways during embryonic development and in disease states [23; 24; 25]. Only a handful of studies have demonstrated a regulatory role of miRNAs in controlling the expression of PCs [20; 26]. For instance, miR-124 directly represses the expression of PACE4 and reduces the cell growth and cell invasion of prostate cancer [27].