Cloning and Initial Characterization of Mouse Meltrin β and Analysis of the Expression of Four MetalloproteaseDisintegrins in Bone Cells

Abstract

Here we report the cloning and initial biochemical characterization of the mouse metalloprotease/disintegrin/cysteine-rich (MDC) protein meltrin ␤ and the analysis of the mRNA expression of four MDC genes (meltrin ␣, meltrin ␤, mdc9, and mdc15) in bone cells, including osteoclasts and osteoblasts. Like most other MDC proteins, the predicted meltrin ␤ protein consists of a signal sequence, prodomain, metalloprotease domain with a predicted catalytic site, disintegrin domain, cysteinerich region, epidermal growth factor repeat, transmembrane domain, and cytoplasmic domain with putative signaling motifs, such as potential SH3 ligand domains. Northern blot analysis indicates that meltrin ␤ is widely expressed, with the highest expression in bone, heart, and lung. RNase protection studies revealed expression of all four MDC genes analyzed here in osteoblasts, whereas only mdc9 and mdc15 mRNAs were detectable in osteoclast-like cells generated in vitro. Treatment of primary osteoblasts with 10 nM calcitriol increased meltrin ␤ expression more than 3-fold, and both meltrin ␣ and meltrin ␤ expression is apparently regulated in a differentiation-associated manner in a mouse osteoblastic cell line, MC3T3E1. Collectively, these results suggest that meltrin ␣ and meltrin ␤ may play a role in osteoblast differentiation and/or function but are not likely to be involved in osteoclast fusion.Proteins containing a metalloprotease domain, a disintegrin domain, and a cysteine-rich region (MDC 1 proteins, also referred to as ADAMs (1)) are a family of membrane-anchored glycoproteins that are related to soluble snake venom metalloproteases and integrin ligands. MDC proteins have been implicated in a variety of important cellular processes, including sperm-egg and muscle cell membrane binding and fusion (2-6); in neuronal induction, lateral inhibition, and neuronal outgrowth in Drosophila (7-9); and in the release of the membrane-anchored cytokine tumor necrosis factor ␣ (10, 11). The finding that the tumor necrosis factor ␣ convertase is an MDC protein (10, 11) and that Drosophila Kuzbanian may be involved in the intracellular processing Notch (9, 12) raises the intriguing possibility that other membrane-anchored proteins are also processed and/or released by metalloprotease-disintegrin proteins (13). Because several MDC proteins contain potential cytoplasmic signaling motifs, including SH3 ligand domains (1, 14 -16), MDC proteins may also play a role in signaling events, or they may be regulated through interactions with cytoplasmic proteins. At present, over 20 genes encoding MDC proteins have been identified in different species, including Caenorhabditis elegans (17), Drosophila melanogaster (7,8), Xenopus laevis (18, 19), mice (1,6,14,20,21), guinea pigs (1,4,21,22), and humans (10,11,14,15,23). Although the function of many of these proteins remains to be determined, it is clear that different MDC proteins are capable of performing a variety of important tasks. To date, MDC proteins have been implicated in two distinct membrane...

Osteocytes as mechanosensors in the inhibition of bone resorption due to mechanical loading

“…Thus, flow might increase the RANKL1 and RANKL2 expression but decrease RANKL3 expression so that the message level of RANKL is increased but the sRANKL protein as the translational product of RANKL3 is decreased. Alternatively sRANKL may be formed from the enzymatic cleavage of the extracellular domain of a full length RANKL (15,29,34,55). And the flow induced decrease of sRANKL may be the result of the flow exerted posttranscriptional or enzymatic effect on MLO-Y4 cells.…”

Cloning and characterization of ADAM28: evidence for autocatalytic pro-domain removal and for cell surface localization of mature ADAM28

“…Like many other ADAM family members, e.g. MDC9 [24], ADAM12 [27], ADAM13 [39], MDC15 [28][29][30], TACE [10,11] and ADAM19 [31,32], the cytoplasmic tail of ADAM28 contains proline-rich regions which may serve as…”

“…Little is known about the activity or functions of the other 13 ADAMs with a catalytic site consensus sequence, except that seven of them appear to be expressed predominantly in the testis, suggesting a role in sperm function [4,[15][16][17][18][19][20][21][22][23]. ADAMs harbouring a catalytic site that are known to be expressed in somatic cells include MDC9 [24], ADAM10\KUZ [8,9,25], ADAM8\ MS2 [26], ADAM12\meltrin α [27], MDC15 [28][29][30], ADAM17\ TACE (tumour necrosis factor converting enzyme) [10,11] and ADAM19\meltrin β [31,32]. Here we report the cDNA cloning and initial biochemical characterization of the mouse protein ADAM28, a catalytic-site-containing ADAM that is expressed in at least two somatic tissues, mouse epididymis and lung.…”

Roles of Meltrin β/ADAM19 in the Processing of Neuregulin

“…Previously, our group and C. P. Blobel and his colleagues (15,19) cloned an ADAM with a conserved active site of a metalloprotease, meltrin ␤/ADAM19. Meltrin ␤ consists of multiple domains including prodomain, metalloprotease domain, disintegrin domain, cysteine-rich domain, epidermal growth factor (EGF)-like domain, transmembrane domain, and cytoplasmic tail.…”