Mitogen-activated protein kinase (MAPK) pathways are activated by several stimuli and transduce the signal inside cells, generating diverse responses including cell proliferation, differentiation, migration and apoptosis. Each MAPK cascade comprises a series of molecules, and regulation takes place at different levels. They communicate with each other and with additional pathways, creating a signaling network that is important for cell fate determination. In this review, we focus on ERK, JNK, p38 and ERK5, the major MAPKs, and their interactions with PI3K-Akt, TGFβ/Smad and Wnt/β-catenin pathways. More importantly, we describe how MAPKs regulate cell proliferation and differentiation in the rapidly renewing epithelia that lines the gastrointestinal tract and, finally, we highlight the recent findings on nutritional aspects that affect MAPK transduction cascades.

Background: Cachexia is a multifactorial and multiorgan syndrome associated with cancer and other chronic diseases and characterized by severe involuntary body weight loss, disrupted metabolism, inflammation, anorexia, fatigue, and diminished quality of life. This syndrome affects around 50% of patients with colon cancer and is directly responsible for the death of at least 20% of all cancer patients. Systemic inflammation has been recently proposed to underline most of cachexia‐related symptoms. Nevertheless, the exact mechanisms leading to the initiation of systemic inflammation have not yet been unveiled, as patients bearing the same tumour and disease stage may or may not present cachexia. We hypothesize a role for gut barrier disruption, which may elicit persistent immune activation in the host. To address this hypothesis, we analysed the healthy colon tissue, adjacent to the tumour.Methods: Blood and rectosigmoid colon samples (20 cm distal to tumour margin) obtained during surgery, from cachectic (CC = 25) or weight stable (WSC = 20) colon cancer patients, who signed the informed consent form, were submitted to morphological (light microscopy), immunological (immunohistochemistry and flow cytometry), and molecular (quantification of inflammatory factors by Luminex® xMAP) analyses.Results: There was no statistical difference in gender and age between groups. The content of plasma interleukin 6 (IL‐6) and IL‐8 was augmented in cachectic patients relative to those with stable weight (P = 0.047 and P = 0.009, respectively). The number of lymphocytic aggregates/field in the gut mucosa was higher in CC than in WSC (P = 0.019), in addition to those of the lamina propria (LP) eosinophils (P < 0.001) and fibroblasts (P < 0.001). The area occupied by goblet cells in the colon mucosa was decreased in CC (P = 0.016). The M1M2 macrophages percentage was increased in the colon of CC, in relation to WSC (P = 0.042). Protein expression of IL‐7, IL‐13, and transforming growth factor beta 3 in the colon was significantly increased in CC, compared with WSC (P = 0.02, P = 0.048, and P = 0.048, respectively), and a trend towards a higher content of granulocyte‐colony stimulating factor in CC was also observed (P = 0.061). The results suggest an increased recruitment of immune cells to the colonic mucosa in CC, as compared with WSC, in a fashion that resembles repair response following injury, with higher tissue content of IL‐13 and transforming growth factor beta 3.Conclusions: The changes in the intestinal mucosa cellularity, along with modified cytokine expression in cachexia, indicate that gut barrier alterations are associated with the syndrome.

Hormones and growth factors regulate endometrial cell growth. Disrupted transforming growth factor-β (TGF-β) signaling in primary endometrial carcinoma (ECA) cells leads to loss of TGF-β–mediated growth inhibition, which we show herein results in lack of up-regulation of the cyclin-dependent kinase inhibitor p27^Kip1 (p27) to arrest cells in G₁ phase of the cell cycle. Conversely, in normal primary endometrial epithelial cells (EECs), TGF-β induces a dose-dependent increase in p27 protein, with a total 3.6-fold maximal increase at 100 pmol/L TGF-β, which was 2-fold higher in the nuclear fraction; mRNA levels were unaffected. In addition, ECA tissue lysates show a high rate of ubiquitin-mediated degradation of p27 compared with normal secretory-phase endometrial tissue (SE) such that 4% and 89% of recombinant p27 added to the lysates remains after 3 and 20 h, respectively. These results are reflected in vivo as ECA tissue lacks p27 compared with high expression of p27 in SE (P ≤ 0.001). Furthermore, we show that estrogen treatment of EECs causes mitogen-activated protein kinase–driven proteasomal degradation of p27 whereas progesterone induces a marked increase in p27 in both normal EECs and ECA cells. Therefore, these data suggest that TGF-β induces accumulation of p27 for normal growth regulation of EECs. However, in ECA, in addition to enhanced proteasomal degradation of p27, TGF-β cannot induce p27 levels due to dysregulated TGF-β signaling, thereby causing 17β-estradiol–driven p27 degradation to proceed unchecked for cell cycle progression. Thus, p27 may be a central target for growth regulation of normal endometrium and in the pathogenesis of ECA. [Cancer Res 2007;67(3):1007–18]