Metabolism of Thrombospondin 2

doi:10.1074/jbc.271.27.15993

Metabolism of Thrombospondin 2

BINDING AND DEGRADATION BY 3T3 CELLS AND GLYCOSAMINOGLYCAN-VARIANT CHINESE HAMSTER OVARY CELLS*

From the ^‡ Departments of Medicine and Biomolecular Chemistry, University of Wisconsin, Madison, Madison, Wisconsin 53706 and
^§ The Holland Laboratory, Department of Biochemistry, American Red Cross, Rockville, Maryland 20855

^¶ To whom correspondence should be addressed:
Dept. of Medicine and Biomolecular Chemistry, University of Wisconsin, Madison, 1300 University Ave., Madison, WI 53706.
Tel.: 608-262-1576; Fax: 608-263-4969.

Abstract

Thrombospondin 1 (TSP1) and thrombospondin 2 (TSP2) are members of the thrombospondin family that have a similar structural organization but somewhat different functional activities. Iodinated recombinant mouse TSP2 bound to NIH 3T3 cells and was internalized and degraded through a chloroquine-inhibitable pathway. TSP2 degradation was saturable, specific, and similar to the kinetics of degradation of TSP1. Human platelet TSP1, recombinant mouse TSP1, and recombinant mouse TSP2 cross-competed with one another for degradation by 3T3 cells. Degradation of TSP2 was less sensitive to inhibition by heparin than degradation of TSP1. This is in agreement with differences in heparin-binding affinity of the two TSPs. Degradation of TSP2 was slower in cultures of Chinese hamster ovary (CHO) cells lacking heparan sulfate proteoglycans than in wild type CHO cells or in cultures of 3T3 cells treated with heparitinase than in untreated 3T3 cells. Degradation of TSP2 was inhibited by antibodies against the low density lipoprotein receptor-related protein (LRP) or by the 39-kDa receptor-associated protein, a known antagonist of LRP. This study indicates that TSP2 and TSP1 are metabolized by a common internalization and degradation pathway involving heparan sulfate proteoglycan and LRP. Competition for this pathway is a possible mechanism whereby cells can control the levels and ratio of TSP1 and TSP2 in the extracellular milieu.

Footnotes

↵* This research was supported in part by National Institutes of Health Grants HL49111 and HL54462 (to D. F. M.) and GM42581 and HL50787 (to D. K. S.). The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵¹ The abbreviations used are:

TSP

thrombospondin

mTSP

mouse TSP

hTSP

human TSP

CHO

Chinese hamster ovary

DME

high glucose Dulbecco's modified Eagle medium

ELISA

enzyme-linked immunosorbent assay

LRP

low density lipoprotein receptor-related protein

PARP

proline- and arginine-rich protein

PF-4

platelet factor 4

RAP

receptor-associated protein

TGF-β1

transforming growth factor-β1.
- Received November 15, 1995.
- Revision received April 10, 1996.