Morphological Characterization of Lewis Lung Carcinoma (3LL). A Light and Electron Microscopic Study

Whole‑exome sequencing reveals Lewis lung carcinoma is a hypermutated Kras/Nras-mutant cancer with extensive regional mutation clusters in its genome

Lewis lung carcinoma (LLC), as a widely used preclinical cancer model, has still not been genetically and genomically characterized. Here, we performed a whole-exome sequencing analysis on the LLC cell line to elucidate its molecular characteristics and etiologies. Our data showed that LLC originated from a male mouse belonging to C57BL/6L (a transitional strain between C57BL/6J and C57BL/6N) and contains substantial somatic SNV and InDel mutations (> 20,000). Extensive regional mutation clusters are present in its genome, which were caused mainly by the mutational processes underlying the SBS1, SBS5, SBS15, SBS17a, and SBS21 signatures during frequent structural rearrangements. Thirty three deleterious mutations are present in 30 cancer genes including Kras, Nras, Trp53, Dcc, and Cacna1d. Cdkn2a and Cdkn2b are biallelically deleted from the genome. Five pathways (RTK/RAS, p53, cell cycle, TGFB, and Hippo) are oncogenically deregulated or affected. The major mutational processes in LLC include chromosomal instability, exposure to metabolic mutagens, spontaneous 5-methylcytosine deamination, defective DNA mismatch repair, and reactive oxygen species. Our data also suggest that LLC is a lung cancer similar to human lung adenocarcinoma. This study lays a molecular basis for the more targeted application of LLC in preclinical research.

Progesterone limits the tumor-promoting effects of the beta-subunit of human chorionic gonadotropin via non-nuclear receptors

The post-menopausal state in women is associated with increased cancer incidence, the reasons for which remain obscure. Curiously, increased circulating levels of beta-hCG (human chorionic gonadotropin) (a hormonal subunit linked with tumors of several lineages) are also often observed post-menopause. This study describes a previously unidentified interplay between beta-hCG and progesterone in tumorigenesis. Progesterone mediated apoptosis in beta-hCG responsive tumor cells via non-nuclear receptors. The transgenic expression of beta-hCG, particularly in the absence of the ovaries (a mimic of the post-menopausal state) constituted a potent pro-tumorigenic signal. Significantly, the administration of progesterone had significant anti-tumor effects. RNA-seq profiling identified molecular signatures associated with these processes. TCGA analysis revealed correlates between the expression of several newly identified genes and poor prognosis in post-menopausal patients of lung adenocarcinoma, colon adenocarcinoma, and glioblastoma. Specifically in these women, the detection of intra-tumoral/extra-tumoral beta-hCG may serve as a useful prognostic indicator, and treatment with progesterone on its detection may prove beneficial.

Morpho-Functional Study of Vascular Fluorochrome Delivery to Lung and Liver Metastases of Lewis Lung Carcinoma (3Ll)

The growth of 3LL liver and lung metastases related to Its vascular organization was studied by morphological and functional methods, using the Hoechst 33342 fluorescent DNA staining technique. Experimental liver and lung metastases were produced in syngeneic C57BL/6 mice by injection of 3LL tumor cells into a lateral tail vein or into the spleen, respectively. The resulting neoplasms were composed of large cells arranged in sheets with a thin irregularly distributed stroma. Scattered blood vessels with an open or closed lumen were observed within the tumor. Functional study of H33342 diffusion showed a single and reticular fluorescent pattern in liver metastases. In contrast, in lung metastases the fluorochrome diffusion revealed two different fluorescent patterns related to the location of the metastasis. Thus, parenchymal and subpleural metastasis presented a fluorescent pattern similar to that observed in the liver whereas metastases located around blood vessels and conducting airways never displayed fluorescence. In summary, our results suggest that the target metastatic organ and/or intra-organ location modulates the characteristics of metabolic exchange of the tumor cells In relation to the vascular organization of the metastatic focus.

Acidic extracellular pH promotes epithelial mesenchymal transition in Lewis lung carcinoma model

Background

Epithelial mesenchymal transition (EMT) is thought to be an essential feature of malignant tumor cells when they spread into the stroma. Despite the extracellular acidity of tumor tissues, the effect of acidic extracellular pH (pH_e) on EMT in carcinoma models, including the Lewis lung carcinoma (LLC) model, remains unclear.

Methods

High and low metastatic LLC variants were generated by repeated tail vein injection of metastatic cells. DMEM/F12 medium, which has been supplemented with 15 mM HEPES, 4 mM phosphoric acid, and 1 g/L NaHCO₃ and adjusted to the desire pH with HCl or NaOH, was used for cell culture. EMT marker gene expression was determined by quantitative reverse transcription-polymerase chain reaction. Migration and invasion activities were analyzed by wound healing assay and the Boyden chamber assay through Matrigel®, respectively.

Results

Low metastatic variant LLCm1 cells showed a cobble-stone like morphology at pH_e 7.4. At pH_e 6.8, however, their morphology became fibroblastic, similar in shape to high metastatic variant LLCm4 cells. Steady state levels of matrix metalloproteinase-9 (Mmp9) mRNA were induced by acidic pH_e, maximizing at pH 6.8, with the levels of Mmp9 mRNA higher in LLCm4 than in LLCm1 cells. Both variants showed decreased levels of E-cadherin and increased levels of vimentin at pH_e 6.8. Acidic pH_e also induced expression of mRNAs encoding the E-cadherin repressors, Zeb2, Twist1 and Twist2, as well as enhancing cell motility and in vitro invasion through Matrigel®.

Conclusions

Acidic pH_e can induce EMT in some types of carcinoma.

Morphological characteristics of tumours formed by Lewis lung carcinoma-derived cloned cell lines with different metastatic potentials: structural differences in their basement membranes formed in vivo

Tumour basement membrane (BM) is an extracellular matrix produced by tumour cells of epithelial origin. We examined the structure and function of the tumour BM of tumour tissues formed by Lewis lung carcinoma-derived cloned cell lines (P29, LM12-3 and LM60-D6 cells) with low, medium and high metastatic potentials, respectively. Immunohistochemical staining of major BM constituents laminin and type IV collagen demonstrated that all the cell lines produced and deposited these materials extracellularly in vivo. However, the continuity of the tumour BM composed of these materials was much greater in the higher metastatic LM12-3 and LM60-D6 tumours than in those with the low metastatic P29 tumour. Electron microscopic examination revealed that in the higher metastatic tumours, especially the LM60-D6 tumour, the tumour BM had a highly organized structure consisting of lamina densa and lamina rara. Parallel bilayers of BM and their fusion were often observed and tumour cells were in direct contact with the BM. In the vicinity of tumour blood vessels, similar interactions between the tumour BM and the vascular BM were observed, and the tumour cells rested on their own BM, the fused BM or the vascular BM. In contrast, in the low metastatic tumour in which the tumour BM was not clearly defined, this close contact between tumour cells and the vascular BM was not observed. In vitro studies showed that the higher metastatic cells adhered more firmly than the LMP cells to a subendothelial matrix. These results suggest that the adhesiveness of tumour cells to the vascular BM in vivo is correlated with their ability to form an integrated BM in vivo, and that this adhesiveness of the tumour cells may be mediated in part by the tumour BM via BM fusion.