Characterization of zinc-?2-glycoprotein as a cell adhesion molecule that inhibits the proliferation of an oral tumor cell line

Abstract

Zn-␣ 2 -glycoprotein (Zn␣ 2 gp) is a soluble protein widely distributed in body fluids and glandular epithelia. We have found it to be expressed in stratified epithelia as well. Zn␣ 2 gp is clinically correlated with differentiation in various epithelial tumors, including oral and epidermal tumors. We have cloned epidermal Zn␣ 2 gp and report the preparation of the recombinant protein in a Baculovirus expression system. Like the native molecule, recombinant Zn␣ 2 gp has RNase activity. Zn␣ 2 gp functions as a matrix protein for the Tu-138 oral squamous cell carcinoma cell line. Cell attachment to Zn␣ 2 gp is comparable to that for fibronectin and is inhibited by the synthetic RGD peptides RGD, RGDV, and RGDS. Attachment is also inhibited by the antibody to integrin ␣ 5 ␤ 1 (the fibronectin receptor), but not by antibodies to integrins ␣ v ␤ 3 , ␣ 3 ␤ 1 , and ␣ 2 ␤ 1 . We find that the proliferation of Tu-138 cells is inhibited on a Zn␣ 2 gp matrix, as compared with other matrix proteins (fibronectin, vitronectin, laminin, and collagens I and IV) on which growth resembles that on the BSA control. We believe that the role of Zn␣ 2 gp in differentiation and its RNase activity are two likely suspects as agents of the inhibition of proliferation.

Zag Expression during Aging Suppresses Proliferation after Kidney Injury

“…12 Consistent with this possibility, several pathologic states associated with an increase in epithelial cell proliferation, including psoriasis 7 and polycystic kidney disease, 26 are accompanied by decreased Zag abundance. This putative antiproliferative effect of Zag has also been demonstrated in vitro in several carcinoma cell lines, 11,12 as well as hepatic stellate cells, bovine endothelial cells, and 3T6 fibroblasts. 17 Although our in vivo studies of I/R revealed that Zag knockdown indeed resulted in improved tubular cell proliferation after I/R injury, these mice did not exhibit accelerated renal recovery.…”

“…Higher levels of Zag expression have been demonstrated to correlate with reduced epithelial proliferation in tumor-derived cells 11,12 ; therefore, for examination of whether Zag might contribute to the age-dependent decline in renal epithelial proliferative repair, the mRNA for murine Zag was cloned and transfected into HEK293 cells, yielding supernatants containing high levels of Zag ( Figure 3F, insert). Addition of Zagenriched supernatant to the culture medium of freshly isolated PT from young kidneys resulted in a significant inhibition of PTEC colony growth ( Figure 3F).…”

“…Using a microarray approach, we found that old kidneys displayed increased proximal tubular expression of zinc-␣ (2)-glycoprotein (Zag), which was previously implicated in epithelial proliferative inhibition. 11,12 The addition of recombinant Zag to primary renal epithelial cell cultures decreased proliferation rates, whereas knockdown of Zag increased proliferation in vitro. In vivo, we found that suppression of tubular Zag expression in aged mice resulted in higher rates of epithelial cell proliferation during the repair phase after ischemia/reperfusion (I/R); however, this desired effect was accompanied by increased parenchymal fibrosis, with no net functional benefit.…”

Zinc α2-Glycoprotein: A Multidisciplinary Protein

“…Finally, Ogikubo et al (126) identified the amino acid sequence accelerating ZAG-mediated MC3T3-E1 cell adhesion and suggested that this region mainly interacted with the cell surface integrins to regulate cell attachment and spreading. Cell attachment to ZAG is comparable with that for fibronectin and is inhibited by the synthetic RGD peptides RGD, RGDV, and RGDS (102).…”

“…Due to the presence of Arg-Gly-Asp (residues 231-233) in a3 domain, it may attain the properties of cell adhesion between cells and extracellular matrices (102). Based on the RGDV sequence, Takagaki et al (122) showed the attachment and spreading of various cells on ZAG-coated plates, and they found very less cell spreading compared with fibronectin, laminin, fibrinogen, and vitronectin.…”