Matrix Metalloproteinase 20–Dentin Sialophosphoprotein Interaction in Oral Cancer

Abstract

Matrix metalloproteinase 20 (MMP-20), widely regarded as tooth specific, participates with MMP-2 in processing dentin sialophosphoprotein (DSPP) into dentin sialoprotein, dentin phosphoprotein, and dentin glycoprotein. In biochemical system, MMP-2, MMP-3, and MMP-9 bind with high affinity to, and are activated by, specific small integrin-binding ligand N-linked glycoproteins (SIBLINGs): bone sialoprotein, osteopontin, and dentin matrix protein 1, respectively. Subsequent reports documented possible biological relevance of SIBLING-MMP interaction in vivo by showing that SIBLINGs are always coexpressed with their MMP partners. However, the cognate MMPs for 2 other SIBLINGs-DSPP and matrix extracellular phosphogylcoprotein-are yet to be identified. Our goal was to investigate MMP-20 expression and to explore preliminary evidence of its interaction with DSPP in oral squamous cell carcinomas (OSCCs). Immunohistochemistry analysis of sections from 21 cases of archived human OSCC tissues showed immunoreactivity for MMP-20 in 18 (86%) and coexpression with DSPP in all 15 cases (71%) positive for DSPP. Similarly, 28 (93%) of 30 cases of oral epithelial dysplasia were positive for MMP-20. Western blot and quantitative real-time polymerase chain reaction analysis on OSCC cell lines showed upregulation of MMP-20 protein and mRNA, respectively, while immunofluorescence showed coexpression of MMP-20 and DSPP. Colocalization and potential interaction of MMP-20 with dentin sialoprotein was confirmed by coimmunoprecipitation and mass spectrometry analysis of immunoprecipitation product from OSCC cell lysate, and in situ proximity ligation assays. Significantly, results of chromatin immunoprecipation revealed a 9-fold enrichment of DSPP at MMP-20 promoter-proximal elements. Our data provide evidence that MMP-20 has a wider tissue distribution than previously acknowledged. MMP-20-DSPP specific interaction, excluding other MMP-20-SIBLING pairings, identifies MMP-20 as DSPP cognate MMP. Furthermore, the strong DSPP enrichment at the MMP-20 promoter suggests a regulatory role in MMP-20 transcription. These novel findings provide the foundation to explore the mechanisms and significance of DSPP-MMP-20 interaction in oral carcinogenesis.

Matrix metalloproteinases in head and neck cancer: current perspectives

“…[22][23][24] Published results from our laboratory show SIBLINGs with known MMP partners coexpressing and colocalizing with their cognate MMP partners in highly metabolic duct epithelial systems of the salivary gland and nephron, and in OSCC cells (DSPP-MMP20 in Figure 3E). …”

“…[18][19][20][21][22] It is a proteolytic enzyme critical for proper dental enamel formation. [18][19][20][21][22] Recently, we reported the expression of MMP20 in oral squamous cell carcinomas (OSCCs) and metabolically active duct epithelial systems of the salivary gland and nephron, indicating that the tissue distribution of MMP20 under physiologic and pathologic conditions may be wider than previously thought. [22][23][24] On the basis of mechanism of regulation, MMPs are classified into three groups: group 1 (MMP1, -3, -7, -9, -12, -19, and -26) contains a TATA box and an activator protein, AP1, which binds to the Fos and Jun family of transcription factors; …”

“…37 Although the cognate MMP partner for MEPE, if any, is yet to be identified, we recently identified MMP20 as the cognate MMP for DSPP. [22][23][24] As depicted in Figure 3, this activation is significant, because the bound SIBLINGs activate their cognate MMP partners, not by removing the inhibitory propeptides, but by inducing a conformational change that lowers the propeptides' affinity for their own binding domain. 36 In consequence, the propeptides vacate the active sites, thereby allowing substrates to be digested ( Figure 3A).…”

“…Ogbureke et al 55 reported that BSP and OPN are overexpressed in OSCCs, accompanied by their known cognate MMP partners: MMP2 and MMP3, respectively. Recently, Saxena et al 22 reported the expression of MMP20 in OSCCs and dysplastic oral premalignant lesions using archived human tissues and cell lines. Hitherto this report, MMP20 expression had been widely regarded as tooth-specific, and thus temporally limited to the odontogenic …”

“…22,56 MMPs are elaborated by malignant epithelial cells, as well as cells of the surrounding stroma, including endothelial cells, fibroblasts, and inflammatory cells. 57 As a result, many studies have examined MMP-expression levels in body fluid, notably serum, as potential diagnostic and prognostic indicators in HNSCC.…”