NOX1 NADPH oxidase regulation by the NOXA1 SH3 domain.
Free Radic Biol Med 2007;
43:384-96. [PMID:
17602954 DOI:
10.1016/j.freeradbiomed.2007.04.022]
[Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/11/2006] [Revised: 04/08/2007] [Accepted: 04/13/2007] [Indexed: 10/23/2022]
Abstract
We investigated the role of the single SH3 domain of NOXA1 in NOX1 NADPH oxidase function using wild-type and mutated NOXA1 and the products of two variant NOXA1 transcripts isolated from CaCo2 cells by reverse transcription polymerase chain reaction. The first variant, NOXA1(trunc), contained a number of point mutations, including A51T, T261A, and a nonsense mutation at position 274. On transfection into K562 cells stably expressing NOX1 and NOXO1, both NOXA1(trunc) and an equivalent truncated wild-type NOXA1(1-273) were expressed as approximately 29-kDa truncated NOXA1 proteins lacking both PB1 and SH3 domains, yet both were as active as wild-type NOXA1 in phorbol-stimulated superoxide generation. Kinetic analysis demonstrated that truncated NOXA1 activated the NOX1 system at an accelerated rate compared with NOXA1. Deletion studies showed that the slower kinetics of wild-type NOXA1 depended primarily on its SH3 domain, suggesting SH3-dependent delay in forming the active NOX1/NOXO1/NOXA1 complex. The second variant, NOXA1(inhib), encoded a protein lacking the activation domain due to absence of exons 5 and 6 but including a heptapeptide (EPDVPLA) SH3 domain insertion resulting from alternative splicing in exon 14. NOXA1(inhib) failed to support superoxide-generating activity and exhibited transdominant inhibition of NOXA1. Insertion of the heptapeptide into the corresponding site in wild-type NOXA1 inhibited its activity by approximately 90%, rendered it a transdominant inhibitor of wild-type NOXA1, and abrogated binding of its SH3 domain to NOXO1 and p47(phox). These studies demonstrate that, in reconstituted NOX1/NOXO1/NOXA1 systems, the NOXA1 SH3 domain is not required for function but, when present, can critically modulate the activity of the enzyme system.
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