Tumor necrosis factor-α (TNFα) released in the brain by HIV-activated macrophages/microglia is suspected to compromise neuronal survival. Previously, we have demonstrated that activated receptor for insulin-like growth factor I (IGF-IR) protects neurons from TNFα-induced neuronal damage (Wang et al. [ 2006] J. Neurosci. Res. 83:7–18). Because TNFα triggers phosphorylation of insulin receptor substrate 1 (IRS-1) on serine residues (pS-IRS-1; Rui et al. [ 2001] J. Clin. Invest. 107:181–189), and pS-IRS-1 binds integrins (Reiss et al. [ 2001] Oncogene 20:490–500), we asked how these events affect neuronal processes. We show that β1-integrin and pS-IRS-1 colocalize in PC12 cells and in primary cortical neurons. TNFα treatment elevated membrane-associated pS-IRS-1, enhanced pS-IRS-1 interaction with β1-integrin, and attenuated cell attachment to collagen IV. In contrast, IGF-I inhibited pS-IRS-1–β1-integrin complexes and improved cell attachment. The domain of IRS-1 involved in β1-integrin binding mapped between amino acids 426 and 740, and the expression of 426–740/IRS-1 mutant attenuated neuronal outgrowth. Our results indicate that TNFα facilitates the interaction of pS-IRS-1 and β1-integrin and destabilizes neuronal processes. IGF-I counteracts TNFα-mediated accumulation of pS-IRS-1–β1-integrin complexes supporting the stability of neuronal processes. © 2007 Wiley-Liss, Inc.