A nuclear target for interleukin-1α: Interaction with the growth suppressor necdin modulates proliferation and collagen expression

Abstract

There is growing evidence for the intracellular role of cytokines and growth factors, but the pathways by which these activities occur remain largely obscure. Previous work from our laboratory identified the constitutive, aberrant expression of the 31-kDa IL-1␣ precursor (pre-IL-1␣) in the nuclei of fibroblasts from the lesional skin of patients with systemic sclerosis (SSc). We established that pre-IL-1␣ expression was associated with increased fibroblast proliferation and collagen production. Further investigation has led to the identification of a mechanism by which nuclear expression of pre-IL-1␣ affects fibroblast growth and matrix production. By using a yeast two-hybrid method, we found that pre-IL-1␣ binds necdin, a nuclear protein with growth suppressor activity. We mapped the region of pre-IL-1␣ responsible for necdin binding and found it to be localized near the N terminus, a region that is present on pre-IL-1␣, but not the mature 17-kDa cytokine. Expression studies demonstrated that pre-IL-1␣ associates with necdin in the nuclei of mammalian cell lines and regulates cell growth and collagen expression. Our results provide the first evidence, to our knowledge, of a nuclear target for pre-IL-1␣. Based on these findings, we propose that the constitutively up-regulated expression of pre-IL-1␣ in the nuclei of SSc fibroblasts up-regulates proliferation and matrix production of SSc fibroblasts through binding necdin, and by counteracting its effects on cell growth and collagen production. IL-1␣ is a pleiotropic cytokine that has numerous effects on the growth and activation on a wide variety of cell types (1). Pre-IL-1␣ is the precursor of mature IL-1␣ containing a nuclear localization sequence (NLS) in its N-terminal region. Processing of the 31-kDa pre-IL-1␣ to the 17-kDa mature form requires the membrane-associated cysteine proteases called calpains, and a variety of cells appear to be deficient in this processing (1). Several studies (2-8) indicate that pre-IL-1␣ accumulates as an intracellular precursor molecule with a molecular mass of 31-kDa in epithelial cells (keratinocytes) and some mesenchymal cells (i.e., endothelial cells and fibroblasts). Previous reports indicate that intracellular pre-IL-1␣ may serve as a regulator of cell growth, senescence, and differentiation (2-9) through an intracrine mechanism (10-16), through interaction with as yet unidentified intracellular target(s).Fibrosis is one of the key features of systemic sclerosis (SSc), and is caused by increased proliferation and extracellular matrix production by fibroblasts of SSc patients (17,18). In contrast to healthy adult human skin fibroblasts, SSc fibroblasts are resistant to the induction of quiescence by serum deprivation, continuing to synthesize DNA, and to express the immediate response protooncogene, c-myc (19). Previous reports (17)(18)(20)(21)(22)(23)(24) have indicated that IL-1␣ increases fibroblast proliferation and collagen production. SSc fibroblasts constitutively express pre-IL-1␣ (2, 25), and the distribution of ...

Biomimetic Delivery of Keratinocyte Growth Factor upon Cellular Demand for Accelerated Wound Healing in Vitro and in Vivo

“…46,47,50 However, the activity of the fusion protein may also be affected if the binding site is localized near the N-or C-terminus, as is the case with interleukin-1␣ and IGF-II. 58,59 Therefore, the Figure 5. Fluorescence imaging of wounds in vivo.…”

The precursor form of IL-1α is an intracrine proinflammatory activator of transcription

“…Using the yeast two-hybrid system, other investigators have reported that pIL-1␣ binds to a nuclear protein called necdin, which possesses growth suppressor activity (29). In mammalian cells pIL-1␣ can associate with necdin to reverse its negative effect on cell growth and production of procollagen (29).…”

“…In mammalian cells pIL-1␣ can associate with necdin to reverse its negative effect on cell growth and production of procollagen (29). Also using the two-hybrid method, ppIL-1␣ has been shown to associate with HAX-1 (30).…”

Intracellular IL-1α-binding proteins contribute to biological functions of endogenous IL-1α in systemic sclerosis fibroblasts

“…A previous investigation looking for a nuclear target of pre-IL-1␣ revealed the interaction between pre-IL-1␣ and necdin by a yeast two-hybrid system (26). Necdin is a 47-kDa protein that functions as a cell-growth suppressor in a manner similar to that of the retinoblastoma tumor suppressor protein, Rb (27,28).…”