Regulation of Cell Proliferation and Migration by TAK1 via Transcriptional Control of von Hippel-Lindau Tumor Suppressor

Abstract

Skin maintenance and healing after wounding requires complex epithelial-mesenchymal interactions purportedly mediated by growth factors and cytokines. We show here that, for wound healing, transforming growth factor-␤-activated kinase 1 (TAK1) in keratinocytes activates von Hippel-Lindau tumor suppressor expression, which in turn represses the expression of platelet-derived growth factor-B (PDGF-B), integrin ␤1, and integrin ␤5 via inhibition of the Sp1-mediated signaling pathway in the keratinocytes. The reduced production of PDGF-B leads to a paracrine-decreased expression of hepatocyte growth factor in the underlying fibroblasts. This TAK1 regulation of the double paracrine PDGF/hepatocyte growth factor signaling can regulate keratinocyte cell proliferation and is required for proper wound healing. Strikingly, TAK1 deficiency enhances cell migration. TAK1-deficient keratinocytes displayed lamellipodia formation with distinct microspike protrusion, associated with an elevated expression of integrins ␤1 and ␤5 and sustained activation of cdc42, Rac1, and RhoA. Our findings provide evidence for a novel homeostatic control of keratinocyte proliferation and migration mediated via TAK1 regulation of von Hippel-Lindau tumor suppressor. Dysfunctional regulation of TAK1 may contribute to the pathology of non-healing chronic inflammatory wounds and psoriasis.Wound healing is a highly dynamic process that involves complex interactions of extracellular matrix molecules, soluble mediators, various resident cells, and infiltrating leukocyte subtypes. The immediate goal in repair is to achieve tissue integrity and homeostasis. The healing process involves three phases that overlap in time and space, namely inflammation, re-epithelialization, and tissue remodeling. Re-epithelialization is accomplished by increased keratinocyte proliferation and guided migration of the keratinocytes over the granulation tissue. Such processes require ordered changes in keratinocyte behavior and phenotype, which are dictated by the interplay of keratinocytes with dermal fibroblasts, i.e. epithelial-mesenchymal communication. This complex interplay demands the integration of diverse signals through a network of soluble factors exerting autocrine and paracrine activity from the wound microenvironment, culminating in appropriate cellular responses (1, 2). Aberrations to this signaling network may impair or enhance cell migration and proliferation, leading to insufficient or excessive wound repair and life-threatening consequences such as tumor growth and metastasis. Therefore, to understand the effect of any molecule in normal cellular function, studies into its role in this signaling network and how they culminate to an appropriate cell response become fundamental and necessary.Transforming growth factor-␤ (TGF-␤) 4 -activated kinase 1 (TAK1) belongs to the MAPK kinase kinase family. This serine/ threonine kinase is a key intermediate in inflammatory cytokines tumor necrosis factor-␣ (TNF-␣) and interleukin 1 (IL-1) (3, 4) as well as TGF-␤ (5)-m...

TAK1 regulates SCF expression to modulate PKBα activity that protects keratinocytes from ROS-induced apoptosis

“…Our previous work has shown that this knockdown is specific and can be rescued by transfection with TAK1 cDNA. 10 The overall epidermal thickness between K CTRL and K TAK1 OTCs was similar, but the suprabasal layer of the K TAK1 epidermis was significantly thinner when compared with K CTRL OTC, as evidenced by immunofluorescence staining for involucrin, a marker of keratinocyte terminal differentiation expressed only in the suprabasal layers of epidermis (Figure 1c). 16 Notably, ROS production was elevated in the K TAK1 -derived epithelia, as revealed by DCF staining (Figure 1c).…”

“…We have previously provided in vivo evidence that the expression of TAK1 is elevated in skin wound biopsies, which peaks at days 3-7 post-injury. 10 To establish a causal relationship between TAK1 and ROS production profile in wound healing, we stained wound biopsies with the fluorescent dye CM-H2DCFDA (DCF). The staining revealed that the wound epithelia were a major site of ROS production that peaked at 3-7 days post-injury, coincident with elevated expression of TAK1 (Figures 1a and b).…”

“…Our previous findings also show that TAK1-deficient keratinocytes have reduced NF-kB activation and pVHL expression. 10 Interestingly, analysis of skin biopsies from patients with psoriasis shows that c-Jun and pVHL are downregulated in psoriatic skin. 33,34 Furthermore, a mouse model of psoriasis is also deficient in epidermal Jun proteins.…”

“…We have previously shown that epidermal TAK1 modulates a double paracrine PDGF/HGF signaling to regulate keratinocyte proliferation that is required for proper wound healing. 10 Specifically, K TAK1 -derived epidermis showed increased proliferation when compared with K CTRL -derived epidermis as a result of the paracrine induction of dermal fibroblasts by keratinocyte-secreted PDGF-B. To rule out the probable influences exerted by this paracrine PDGF-mediated pathway, anti-PDGF antibodies were added as a control.…”

“…10 In the skin, these downstream mediators of TAK1 are important for the maintenance of epidermal homeostasis. 10,11 Perturbations to the JNK pathway have been implicated in epidermal hyperplasia leading to cancer development, while reduced NF-kB function is linked to epidermal squamous cell carcinoma. Blocking the NF-kB pathway through IKKb or IKKg inactivation also leads to severe skin inflammation.…”