Lack of integrin α-chain endoproteolytic cleavage in furin-deficient human colon adenocarcinoma cells LoVo

Abstract

In the present report the biosynthesis of the integrin alpha-chains endowed with constitutive endoproteolytic cleavage was evaluated in LoVo cells where furin, a subtilisin-like convertase involved in post-translational endoproteolytic processing, is not functional. It was found that cell-surface alpha 3, alpha 6 and alpha v subunits were not processed endoproteolytically into heavy and light chains as they were in HT29-D4 cells, a furin-competent cell line. Complete removal of N-linked oligosaccharides and pulse-chase experiments confirmed that the cleavage of the alpha 6 integrin subunit occurring 45 min after translation in HT29 cells did not take place in LoVo cells. Apart from cleavage deficiency, alpha 6 subunit glycosylation, association with beta 4 subunits and targeting to the plasma membrane seemed comparable in LoVo and HT29 cells. The pro-alpha 6 and the pro-alpha 3 subunits immunopurified from LoVo cells were highly sensitive to endoproteolysis by recombinant furin. Furin cleavage was calcium dependent and resulted in the conversion of the 140 kDa pro-alpha 6 into a 120 kDa heavy chain. These results suggest strongly that furin is involved in the endoproteolytic processing of cleavable integrin alpha subunits.

A Systematic Study of Site-specific GalNAc-type O-Glycosylation Modulating Proprotein Convertase Processing

“…Integrins are transmembrane cell surface ␣/␤ heterodimeric receptors of which two, platelet glycoprotein IIb (36) and integrin ␤1 (37), are known to be O-glycosylated and several ␣-integrin subunits undergo PC processing by furin in the extracellular domain yielding disulfide-linked heavy and light chains (38). Integrin ␣E (CD103) heterodimerizes with integrin ␤7 (␣E␤7) and constitutes the E-cadherin binding integrin, also known as mucosal lymphocyte-1 antigen, primarily expressed in intestinal intraepithelial lymphocytes.…”

Proprotein convertase furin/PCSK3 and atherosclerosis: New insights and potential therapeutic targets

“…The redundant function of furin is responsible for the endoproteolytic processing of the integrin pro-a subunits. The recombinant furin can also mediate the endoproteolysis of pro-a 6 and the pro-a 3 subunits from LoVo cells [65]. Integrin a 6 and a 3 subunits are mainly expressed in T cells, monocytes and B cells [66], suggesting the potential roles for furin in the accumulation of these inflammatory cells in the early atherosclerotic lesions.…”

An Alternative Processing of Integrin αv Subunit in Tumor Cells by Membrane Type-1 Matrix Metalloproteinase

“…PC cleavage converts single chain ␣ precursors into respective mature subunits consisting of an N-terminal heavy chain and a C-terminal light chain connected by a disulfide bridge (7). Furin, a member of the PC family, has been specifically implicated in the cleavage of pro-␣ 5 , -␣ 6 , and -␣ v chains (7,8). The role of this cleavage in integrin function is unclear.…”