Membrane Localization of Membrane Type 1 Matrix Metalloproteinase by CD44 Regulates the Activation of Pro-Matrix Metalloproteinase 9 in Osteoclasts

Tao Ma,Meenakshi A Chellaiah

doi:10.1155/2013/302392

Tao Ma, Meenakshi A Chellaiah

Open Access

https://doi.org/10.1155/2013/302392

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Abstract

CD44, MT1-MMP, and MMP9 are implicated in the migration of osteoclast and bone resorption. This study was designed to determine the functional relationship between CD44 and MT1-MMP in the activation of pro-MMP9. We used osteoclasts isolated from wild-type and CD44-null mice. Results showed that MT1-MMP is present in multiple forms with a molecular mass ~63, 55, and 45 kDa in the membrane of wild-type osteoclasts. CD44-null osteoclasts demonstrated a 55 kDa active MT1-MMP form in the membrane and conditioned medium. It failed to activate pro-MMP9 because TIMP2 binds and inhibits this MT1-MMP (~55 kDa) in CD44-null osteoclasts. The role of MT1-MMP in the activation of pro-MMP9, CD44 expression, and migration was confirmed by knockdown of MT1-MMP in wild-type osteoclasts. Although knockdown of MMP9 suppressed osteoclast migration, it had no effects on MT1-MMP activity or CD44 expression. These results suggest that CD44 and MT1-MMP are directly or indirectly involved in the regulation of pro-MMP9 activation. Surface expression of CD44, membrane localization of MT1-MMP, and activation of pro-MMP9 are the necessary sequence of events in osteoclast migration.

Highlights

Matrix metalloproteinases (MMPs) are a group of endopeptidases that regulate osteoclast migration and bone resorption [1,2,3]
MMP antibody microarray was bought from Ray Biotech Inc. (Norcross, CA., USA, Cat. number: HO149801) Antibodies to CD44 standard (CD44s), MT1-MMP, tissue inhibitor of metalloproteinases (TIMPs)-2, and MMP9 were purchased from Santa Cruz Laboratory
Reverse zymogram analysis of the lower half of the zymogram gel demonstrated a protein with molecular mass ∼24–27 kDa (Figure 1(b)) which was confirmed as TIMP2 in immunoblotting analysis (Figure 1(d))

Summary

Introduction

Matrix metalloproteinases (MMPs) are a group of endopeptidases that regulate osteoclast migration and bone resorption [1,2,3]. MMP9 has been proven to be indispensable for the migration of osteoclasts through collagen both in periosteum and developing marrow cavity of primitive long bones [5]. Long bones of MMP9-knockout mice are 10% shorter than bones from wild-type mice [6]. Osteoblasts express MMP2, and bones of MMP2-knockout mice are lower in bone mineral density than those of wildtype mice. Observations in these knockout mice suggest that MMP2 and MMP9 may have a compositional and structural influence, respectively, on the biomechanical properties of whole bones

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