The LIM-domain only protein 4 contributes to lung epithelial cell proliferation but is not essential for tumor progression.

BACKGROUND: The lung is constantly exposed to environmental challenges and must rapidly respond to external insults. Mechanisms involved in the repair of the damaged lung involve expansion of different epithelial cells to repopulate the injured cellular compartment. However, factors regulating cell proliferation following lung injury remain poorly understood. Here we studied the role of the transcriptional regulator Lmo4 during lung development, in the regulation of adult lung epithelial cell proliferation following lung damage and in the context of oncogenic transformation. METHODS: To study the role of Lmo4 in embryonic lung development, lung repair and tumorigenesis, we used conditional knock-out mice to delete Lmo4 in lung epithelial cells from the first stages of lung development. The role of Lmo4 in lung repair was evaluated using two experimental models of lung damage involving chemical and viral injury. The role of Lmo4 in lung tumorigenesis was measured using a mouse model of lung adenocarcinoma in which the oncogenic K-Ras protein has been knocked into the K-Ras locus. Overall survival difference between genotypes was tested by log rank test. Difference between means was tested using one-way ANOVA after assuring that assumptions of normality and equality of variance were satisfied. RESULTS: We found that Lmo4 was not required for normal embryonic lung morphogenesis. In the adult lung, loss of Lmo4 reduced epithelial cell proliferation and delayed repair of the lung following naphthalene or flu-mediated injury, suggesting that Lmo4 participates in the regulation of epithelial cell expansion in response to cellular damage. In the context of K-Ras(G12D)-driven lung tumor formation, Lmo4 loss did not alter overall survival but delayed initiation of lung hyperplasia in K-Ras(G12D) mice sensitized by naphthalene injury. Finally, we evaluated the expression of LMO4 in tissue microarrays of early stage non-small cell lung cancer and observed that LMO4 is more highly expressed in lung squamous cell carcinoma compared to adenocarcinoma. CONCLUSIONS: Together these results show that the transcriptional regulator Lmo4 participates in the regulation of lung epithelial cell proliferation in the context of injury and oncogenic transformation but that Lmo4 depletion is not sufficient to prevent lung repair or tumour formation.

Platelet-Specific PDGFB Ablation Impairs Tumor Vessel Integrity and Promotes Metastasis.

Platelet-derived growth factor B (PDGFB) plays a crucial role in recruitment of PDGF receptor ß-positive pericytes to blood vessels. The endothelium is an essential source of PDGFB in this process. Platelets constitute a major reservoir of PDGFB and are continuously activated in the tumor microenvironment, exposing tumors to the plethora of growth factors contained in platelet granules. Here, we show that tumor vascular function, as well as pericyte coverage is significantly impaired in mice with conditional knockout of PDGFB in platelets. A lack of PDGFB in platelets led to enhanced hypoxia and epithelial-to-mesenchymal transition in the primary tumors, elevated levels of circulating tumor cells, and increased spontaneous metastasis to the liver or lungs in two mouse models. These findings establish a previously unknown role for platelet-derived PDGFB, whereby it promotes and maintains vascular integrity in the tumor microenvironment by contributing to the recruitment of pericytes. SIGNIFICANCE: Conditional knockout of PDGFB in platelets demonstrates its previously unknown role in the maintenance of tumor vascular integrity and host protection against metastasis.

PFKM gene defect and glycogen storage disease GSDVII with misleading enzyme histochemistry.

OBJECTIVE: To elaborate the diagnostic methods used as "gold standard" in one of the most common glycogen storage diseases (GSDs), Tarui disease (GSDVII). METHODS: Two siblings with disease suggestive of GSD underwent thorough clinical analysis, including muscle biopsy, muscle MRI, exercise tests, laboratory examinations, and whole-exome sequencing (WES). RESULTS: Both siblings had juvenile-onset exercise intolerance with cramping and infrequent myoglobinuria. Muscle biopsy showed extralysosomal glycogen accumulation, but because of normal phosphofructokinase histochemistry, GSDVII was thought to be excluded. However, WES revealed a causative homozygous PFKM gene defect, R39Q, in both siblings, establishing the diagnosis of GSDVII, which was confirmed by very low residual phosphofructo-1-kinase (PFK) enzyme activity in biochemical studies. CONCLUSIONS: We suggest that in patients with suspicion of GSD and extralysosomal glycogen accumulation, biochemical activity assay of PFK followed by molecular genetics should be performed even when enzyme histochemistry is normal.