Slaymi Chaker, Vignal Emmanuel, Crès Gaëlle, Roux Pierre, Blangy Anne, Raynaud Peggy, Fort Philippe
CRBM, CNRS, University of Montpellier, 34293, Montpellier CEDEX 5, France.
Biol Cell. 2019 May;111(5):121-141. doi: 10.1111/boc.201800062. Epub 2019 Mar 12.
The mammalian gut epithelium displays among the highest rates of self-renewal, with a turnover time of less than 5 days. Renewal involves concerted proliferation at the bottom of the crypt, migration and differentiation along the crypt-villus axis and anoïkis/shedding in the luminal epithelium. Renewal is controlled by interplay between signalling pathways, among which canonical and non-canonical Wnt signals play prominent roles. Overall 92% of colon tumours show increased canonical Wnt signalling resulting from mutations, established as major driver steps towards carcinogenesis.
Here, we examined the physiological role of RhoU/Wrch1 in gut homeostasis. RhoU is an atypical Rho GTPase related to Cdc42/Rac1 and identified as a transcriptional target of non-canonical Wnt signalling. We found that RHOU expression is reduced in human colorectal tumour samples. We show that RhoU is mainly expressed in the differentiated compartment of the gut epithelium. Rhou specific invalidation in the mouse gut elicits cell hyperplasia and is associated in the colon with a highly disorganized luminal epithelium. Hyperplasia affects all cell types in the small intestine and colon and has a higher impact on goblet cells. Hyperplasia is associated with a reduction of apoptosis and an increased proliferation. RhoU knockdown in human DLD-1 colon cancer cells also elicits a higher growth index and reduces cell apoptosis. Last, loss of RhoU function in the mouse gut epithelium or in DLD-1 cells increases RhoA activity and the level of phosphorylated Myosin Light Chain-2, which may functionally link RhoU activity to apoptosis.
RhoU is mostly expressed in the differentiated compartment of the gut. It plays a role in homeostasis as its specific invalidation elicits hyperplasia of all cell types. This mainly results from a reduction of apoptosis, through actomyosin-dependent mechanisms.
RhoU negatively controls cell growth in the intestinal epithelium. Since its expression is sensitive to non-canonical Wnt signals and is reduced in colorectal tumours, downregulating RhoU may thus have an instrumental role in tumour progression.
哺乳动物肠道上皮细胞的自我更新速度极快，更新周期不到5天。更新过程包括隐窝底部的协同增殖、沿隐窝-绒毛轴的迁移和分化以及管腔上皮细胞的失巢凋亡/脱落。更新受信号通路之间相互作用的控制，其中经典和非经典Wnt信号起着重要作用。总体而言，92%的结肠肿瘤因突变而导致经典Wnt信号增加，这已被确定为致癌的主要驱动步骤。
在此，我们研究了RhoU/Wrch1在肠道稳态中的生理作用。RhoU是一种与Cdc42/Rac1相关的非典型Rho GTP酶，被确定为非经典Wnt信号的转录靶点。我们发现RHOU在人类结直肠癌样本中的表达降低。我们表明RhoU主要在肠道上皮细胞的分化区室中表达。在小鼠肠道中特异性敲除Rhou会引发细胞增生，并且在结肠中与高度紊乱的管腔上皮细胞有关。增生影响小肠和结肠中的所有细胞类型，对杯状细胞的影响更大。增生与细胞凋亡减少和增殖增加有关。在人DLD-1结肠癌细胞中敲低RhoU也会引发更高的生长指数并减少细胞凋亡。最后，小鼠肠道上皮细胞或DLD-1细胞中RhoU功能的丧失会增加RhoA活性和磷酸化肌球蛋白轻链-2的水平，这可能在功能上将RhoU活性与细胞凋亡联系起来。
RhoU主要在肠道的分化区室中表达。它在稳态中发挥作用，因为其特异性敲除会引发所有细胞类型的增生。这主要是通过肌动球蛋白依赖性机制导致细胞凋亡减少。
RhoU对肠道上皮细胞的生长起负调控作用。由于其表达对非经典Wnt信号敏感且在结直肠癌中降低，因此下调RhoU可能在肿瘤进展中起重要作用。
