Functional overexpression of wild-type p53 correlates with alveolar cell differentiation in the developing human lung

Proliferation, apoptosis and expression of matrix metalloproteinase-9 in human fetal lung

Expression pattern of the Ki-67, caspase-3 and matrix metalloproteinases-9 (MMP-9) factors were immunohistochemically analyzed in 48 human fetal lungs from 12 to 40 weeks of gestation. The number of Ki-67 positive cells in the epithelium of canaliculare (88cells/mm(2)) and sacculare stage (93cells/mm(2)) were significantly higher than in the epithelium of pseudoglandular stage (12cells/mm(2)) (p=0.0008 vs. p=0.003). The number of Ki-67 positive cells in the mesenchyme of canaliculare stage (132cells/mm(2)) was significantly higher than in the mesenchyme of pseudoglandular stage (37cells/mm(2)) (p=0.001). The proliferation of mesenchymal cells was higher than the epithelial cells in all developmental stages, especially in the canaliculare stage (p=0.007). Similarly, the number of caspase-3 positive cells in the epithelium of canalicular stage (13cells/mm(2)) was significantly higher than in the epithelium of pseudoglandular stage (6cells/mm(2)) (p=0.002) with peaks in the conductive epithelium of canalicular stage. The number of caspase-3 positive cells in the mesenchyme of canaliculare stage (3cells/mm(2)) was significantly higher than in the mesenchyme of saccular stage (0cells/mm(2)) (p=0.05). There were no caspase-3 positive cells in the mesenchyme of pseudoglandular stage. However, unlike the Ki-67 expression, mesenchymal cells in comparison to epithelial cells express substantially less caspase-3 in all developmental stages. Up to the saccular stage, the expression of MMP-9 in mesenchymal cells showed a linear increase with most pronounced expression in that stage. The number of MMP-9 positive cells in the mesenchyme of canaliculare (20cells/mm(2)) and sacculare (39cells/mm(2)) stage were significantly higher than in the mesenchyme of pseudoglandular stage (12cells/mm(2)) (p=0.04 vs. p=0.004). The first epithelial cells that express MMP-9 were present only at the alveolar stage. Increased proliferation and apoptosis of the mesenchymal cells of canalicular stage is important for formation of definite structures within the stroma of the lung parenchyma. Although apoptosis in the epithelium is not pronounced as proliferation, it is important for thinning of the epithelium and consequent spread of respiratory tract. However in the saccular stage when mesenchyme disappears, MMP-9 expression is more important for primitive alveoli differentiation.

miRNA regulated pathways in late stage murine lung development

Background

MicroRNAs play important roles in regulating biological processes, including organ morphogenesis and maturation. However, little is known about specific pathways regulated by miRNA during lung development. Between the canalicular and saccular stages of the developing lung several important cellular events occur, including the onset of surfactant synthesis, microvascular remodeling and structural preparation for subsequent alveolarization. The miRNAs that are actively regulated, and the identity of their targets during this important developmental interval in the lung remain elusive.

Results

Using TLDA low density real-time PCR arrays, the expression of 376 miRNAs in male and female fetal mouse lungs of gestational days E15 – E18 were profiled. Statistical analyses identified 25 and 37 miRNAs that changed significantly between sexes and with gestation, respectively. In silico analysis using Ingenuity Pathway Analysis (IPA) identified specific pathways and networks known to be targets of these miRNAs which are important to lung development. Pathways that are targeted by sex regulated miRNAs include retinoin, IGFR1, Tp53 and Akt. Pathways targeted by gestation-regulated miRNAs include VEGFA and mediators of glucose metabolism.

Conclusion

MiRNAs are differentially regulated across time and between sexes during the canalicular and saccular stages of lung development. Sex-associated differential miRNA expression may regulate the differences in structural and functional male and female lung development, as shown by networks generated using in silico analysis. These data provide a valuable resource to further enhance the understanding of miRNA control of lung development and maturation.

MicroRNA-206 is associated with invasion and metastasis of lung cancer

MicroRNAs are novel small noncoding RNA molecules that regulate gene expression at the post-transcriptional level. Compelling evidence reveals that there is a causative link between microRNAs deregulation and cancer development and progression. The present study aims to explore the function of miR-206 in the proliferation, apoptosis, motility, and invasion of nonsmall cell lung cancer. Using real-time PCR, we detected the miR-206 expression of normal lung tissues, tumor tissues, human normal bronchial epithelial cell line, and six lung cancer cell lines (LCCLs). Then, we evaluated the role of miR-206 in cell proliferation, apoptosis, and invasion using Cell Counting Kit-8 assay, Annexin-V/FITC assay, wound healing, and Transwell assay in LCCLs. As a result, miR-206 expression level was lower in high metastasis tumors and 95D than low metastasis tumors and normal lung tissues as well as other LCCLs. After miR-206 was upregulated in LCCLs, cell proliferation was notably attenuated and apoptosis was significantly increased. Furthermore, overexpression of miR-206 inhibited migration and invasion of lung cancer cells. In conclusion, our data suggest that expression level of miR-206 was inversely correlated with metastatic potential of lung cancer.

NGF-mediated transcriptional targets of p53 in PC12 neuronal differentiation

BACKGROUND

p53 is recognized as a critical regulator of the cell cycle and apoptosis. Mounting evidence also suggests a role for p53 in differentiation of cells including neuronal precursors. We studied the transcriptional role of p53 during nerve growth factor-induced differentiation of the PC12 line into neuron-like cells. We hypothesized that p53 contributed to PC12 differentiation through the regulation of gene targets distinct from its known transcriptional targets for apoptosis or DNA repair.

RESULTS

Using a genome-wide chromatin immunoprecipitation cloning technique, we identified and validated 14 novel p53-regulated genes following NGF treatment. The data show p53 protein was transcriptionally activated and contributed to NGF-mediated neurite outgrowth during differentiation of PC12 cells. Furthermore, we describe stimulus-specific regulation of a subset of these target genes by p53. The most salient differentiation-relevant target genes included wnt7b involved in dendritic extension and the tfcp2l4/grhl3 grainyhead homolog implicated in ectodermal development. Additional targets included brk, sdk2, sesn3, txnl2, dusp5, pon3, lect1, pkcbpb15 and other genes.

CONCLUSION

Within the PC12 neuronal context, putative p53-occupied genomic loci spanned the entire Rattus norvegicus genome upon NGF treatment. We conclude that receptor-mediated p53 transcriptional activity is involved in PC12 differentiation and may suggest a contributory role for p53 in neuronal development.

Uteroplacental insufficiency decreases p53 serine-15 phosphorylation in term IUGR rat lungs

Intrauterine growth restriction (IUGR) increases the incidence of chronic lung disease (CLD). The molecular mechanisms responsible for IUGR-induced acute lung injury that predispose the IUGR infant to CLD are unknown. p53, a transcription factor, plays a pivotal role in determining cellular response to stress by affecting apoptosis, cell cycle regulation, and angiogenesis, processes required for thinning of lung mesenchyme. Because thickened lung mesenchyme is characteristic of CLD, we hypothesized that IUGR-induced changes in lung growth are associated with alterations in p53 expression and/or modification. We induced IUGR through bilateral uterine artery ligation of pregnant rats. Uteroplacental insufficiency significantly decreased serine-15-phosphorylated (serine-15P) p53, an active form of p53, in IUGR rat lung. Moreover, we found that decreased phosphorylation of lung p53 serine-15 localized to thickened distal air space mesenchyme. We also found that IUGR significantly decreased mRNA for targets downstream of p53, specifically, proapoptotic Bax and Apaf, as well as Gadd45, involved in growth arrest, and Tsp-1, involved in angiogenesis. Furthermore, we found that IUGR significantly increased mRNA for Bcl-2, an antiapoptotic gene downregulated by p53. We conclude that in IUGR rats, uteroplacental insufficiency induces decreased lung mesenchymal p53 serine-15P in association with distal lung mesenchymal thickening. We speculate that decreased p53 serine-15P in IUGR rat lungs alters lung phenotype, making the IUGR lung more susceptible to subsequent injury.

Distribution of ERK1/2 and ERK3 during normal rat fetal lung development

The extracellular regulated kinases-1 and -2 (ERK1/2) are well-characterized mitogen-activated protein kinases (MAPK) that play critical roles in proliferation and differentiation, whereas the function(s) of MAPK ERK3 are currently unknown. To understand better the roles of these kinases in development, the temporal distribution of ERK1, -2, and -3 proteins were investigated in multiple tissues. The ERK3 protein, in contrast to ERK1/2 varied both between and within individual organs over time. To characterize this variability in greater detail, the temporal and spatial distributions of activated ERK1/2 and ERK3 during rat fetal lung development were investigated. The diphosphorylated (activated) forms of ERK1/2 (dp-ERK1/2), ERK3, and its phosphorylated form (P-ERK3) decreased from embryonic day 17 (E17) through E21 while both ERK1 and ERK2 total proteins remained unchanged, indicating that ERK1/2 and ERK3 proteins are expressed independently during fetal lung development. In addition, characterization of the distribution of these proteins by fluorescent immunohistochemistry indicated that phosphorylated ERK1/2 and total ERK1/2 were distributed throughout multiple cell types, with the phosphorylated ERK1/2 colocalizing with prophase mitotic cells. In contrast, ERK3 was restricted to the distal lung epithelium during the pseudoglandular phase (E17) but shifted to the proximal airways, particularly Clara cells during the saccular stage (E21). The P-ERK3 colocalized with the mitotic marker P-histone H3 in fetal lung and in NIH3T3 and HeLa cells, implicating a potential role for P-ERK3 in mitosis. Thus, expression of ERK1/2 and ERK3 and their phosphorylated forms are expressed independently and are temporally and spatially localized during fetal lung morphogenesis. These observations will facilitate detailed functional analysis of these kinases to assess their roles in pulmonary development and diseases.

Hyperoxic ventilated premature baboons have increased p53, oxidant DNA damage and decreased VEGF expression

Hyperoxia is implicated in the pathogenesis of bronchopulmonary dysplasia (BPD), a chronic lung disease of premature infants. High levels of supplemental oxygen can result in microvascular endothelial cell death and may disrupt lung development. In postnatal animals, hyperoxia inhibits expression of vascular endothelial growth factor (VEGF), which is required for normal vascular development. A potential mechanism of oxygen effects on VEGF is induction of p53, a transcription factor that represses VEGF gene transcription. Oxidant DNA damage can increase p53. We used a moderately premature baboon model of hyperoxia to examine p53, oxidant DNA damage, and VEGF expression. Fetal baboons delivered at 140 d of gestation (75% of term) were ventilated with 100% oxygen or oxygen as needed for 6 or 10 d. Lungs from the 10-d 100% oxygen animals had increased nuclear p53, compared with the oxygen as needed animals. The mechanism of increased p53 was probably related to oxidant DNA damage, which was documented by increased oxidized guanine. Dual fluorescent confocal microscopy found increased oxidized guanine in mitochondrial DNA of distal lung epithelial cells. Distal epithelial cell VEGF expression was decreased and p21, another downstream target of p53, was increased in the distal epithelium of the hyperoxic animals. These data show that p53 is induced in hyperoxic fetal lung epithelium and are consistent with p53 repression of VEGF expression in these cells. The findings suggest that oxidant DNA damage may be a mechanism of increased p53 in hyperoxic fetal lung.