Transforming Growth Factor β1 Increases p27 Levels via Synthesis and Degradation Mechanisms in the Hyperproliferative Gastric Epithelium in Rats

Abstract

Throughout postnatal development, the gastric epithelium expresses Transforming Growth Factor beta1 (TGFβ1), but it is also exposed to luminal peptides that are part of milk. During suckling period, fasting promotes the withdrawal of milk-born molecules while it stimulates gastric epithelial cell proliferation. Such response can be reversed by exogenous TGFβ1, as it directly affects cell cycle through the regulation of p27 levels. We used fasting condition to induce the hyperproliferation of gastric epithelial cells in 14-day-old Wistar rats, and evaluated the effects of TGFβ1 gavage on p27 expression, phosphorylation at threonine 187 (phospho-p27Thr187) and degradation. p27 protein level was reduced during fasting when compared to suckling counterparts, while phospho-p27Thr187/p27 ratio was increased. TGFβ1 gavage reversed this response, which was confirmed through immunostaining. By using a neutralizing antibody against TGFβ1, we found that it restored the p27 and phosphorylation levels detected during fasting, indicating the specific role of the growth factor. We noted that neither fasting nor TGFβ1 changed p27 expression, but after cycloheximide administration, we observed that protein synthesis was influenced by TGFβ1. Next, we evaluated the capacity of the gastric mucosa to degrade p27 and we recorded a higher concentration of the remaining protein in pups treated with TGFβ1, suggesting augmented stability under this condition. Thus, we showed for the first time that luminal TGFβ1 increased p27 levels in the rat gastric mucosa by up- regulating translation and reducing protein degradation. We concluded that such mechanisms might be used by rapidly proliferating cells to respond to milk-born TGFβ1 and food restriction.

Lifelong Adaptation of Gastric Cell Proliferation and Mucosa Structure to Early Weaning-Induced Effects

“…Conversely, high p27 leads to tumor suppression in gastric cells (Liu et al, 2019 ). We did not find evidence of lesions after EW, but the low levels at 18 days corroborated previous data that showed that p27 can be regulated by different feeding patterns, and it controls cell proliferation in the gastric epithelium (de Andrade Sá et al, 2008 ; Ogias et al, 2010 ; Osaki and Gama, 2013 ; Fiore et al, 2014 ).…”

“…Among cell cycle regulatory molecules, none of the genes were affected, but p27 protein levels behaved similarly to the TGF beta family with a decrease after EW only at 18 days. Different studies demonstrated that, in the gastric epithelia p27 expression, synthesis and degradation are sensitive to changes in the feeding pattern (de Andrade Sá et al, 2008 ; Ogias et al, 2010 ; Osaki and Gama, 2013 ; Fiore et al, 2014 ). Low p27 concentration is a prevalent condition for tumor growth, and its deficiency correlates with gastric (Kuzushita et al, 2005 ) and endometrial cancers (Lecanda et al, 2009 ; Pavlides et al, 2016 ).…”

“…Throughout development, milk-born peptides, together with growth factors synthesized in the gastric gland, contribute to regulate cell cycle and proliferation (de Andrade Sá et al, 2003 ; Osaki et al, 2010 , 2011 ; Osaki and Gama, 2013 ; Fiore et al, 2014 ). Previously, we demonstrated that TGFβ is one of these key regulators for stomach growth (de Andrade Sá et al, 2003 , 2008 ).…”

“…Previously, we demonstrated that TGFβ is one of these key regulators for stomach growth (de Andrade Sá et al, 2003 , 2008 ). During the suckling period, TGFβ activity is balanced and controls p27 levels (de Andrade Sá et al, 2003 ; Fiore et al, 2014 ), but if feeding pattern changes, signaling is disrupted and p27 is degraded more rapidly, increasing the epithelial renewal (de Andrade Sá et al, 2003 ; Fiore et al, 2014 ).…”

The Multifaceted Role of TGF-β in Gastrointestinal Tumors

“…During the early stage of tumorigenesis, TGF-β operates as a tumor suppressor by inducing apoptosis in pre-malignant cells or G1 phase cell cycle arrest in carcinoma cells [48]. Previous studies have implicated p15 INK2B and p27 Kip1 as mediators of the growth inhibitory effect of TGF-β, which act by inhibiting cyclinD1/Cdk4 and cyclinE/Cdk2 complexes, respectively [49,50]. Further, TGF-β has been shown to induce p21 (Waf1, Cip1) through a p53-independent transcriptional regulation [51][52][53] but also by increasing its protein stability, which leads to inhibition of Cdk2 kinase activity [54].…”