LAMC2 marks a tumor-initiating cell population with an aggressive signature in pancreatic cancer

BACKGROUND

Tumor-initiating cells (TIC), also known as cancer stem cells, are considered a specific subpopulation of cells necessary for cancer initiation and metastasis; however, the mechanisms by which they acquire metastatic traits are not well understood.

METHODS

LAMC2 transcriptional levels were evaluated using publicly available transcriptome data sets, and LAMC2 immunohistochemistry was performed using a tissue microarray composed of PDAC and normal pancreas tissues. Silencing and tracing of LAMC2 was performed using lentiviral shRNA constructs and CRISPR/Cas9-mediated homologous recombination, respectively. The contribution of LAMC2 to PDAC tumorigenicity was explored in vitro by tumor cell invasion, migration, sphere-forming and organoids assays, and in vivo by tumor growth and metastatic assays. mRNA sequencing was performed to identify key cellular pathways upregulated in LAMC2 expressing cells. Metastatic spreading induced by LAMC2- expressing cells was blocked by pharmacological inhibition of transforming growth factor beta (TGF-β) signaling.

RESULTS

We report a LAMC2-expressing cell population, which is endowed with enhanced self-renewal capacity, and is sufficient for tumor initiation and differentiation, and drives metastasis. mRNA profiling of these cells indicates a prominent squamous signature, and differentially activated pathways critical for tumor growth and metastasis, including deregulation of the TGF-β signaling pathway. Treatment with Vactosertib, a new small molecule inhibitor of the TGF-β type I receptor (activin receptor-like kinase-5, ALK5), completely abrogated lung metastasis, primarily originating from LAMC2-expressing cells.

CONCLUSIONS

We have identified a highly metastatic subpopulation of TICs marked by LAMC2. Strategies aimed at targeting the LAMC2 population may be effective in reducing tumor aggressiveness in PDAC patients. Our results prompt further study of this TIC population in pancreatic cancer and exploration as a potential therapeutic target and/or biomarker.

Abstract PO-038: LAMC2: New player in stemness and tumor progression in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is a devastating and essentially incurable disease, typically characterized by high chemoresistance and metastatic spread attributable to cancer stem cells (CSCs). This subpopulation is critical for tumor initiation and recurrence, but the mechanism through which they acquire metastatic traits is not well understood. Hence, targeting the CSC niche and their plasticity could be a complementary therapeutic strategy against cancer. Laminin subunit-γ-2 (LAMC2) is an epithelial basement membrane protein, which controls cell motility and adhesion and is widely expressed in the majority of human tumors. However, its role in PDAC remains largely unknown. In several patient cohorts we observed that high levels of LAMC2 significantly correlated with shorter overall survival. In addition, the tissue microarray analysis on PDAC sections revealed prognostic significance of LAMC2 expression in tumor with high grade of aggressiveness (i.e., G2 and G3). To determine the role of LAMC2 in sustaining tumorigenicity, we knocked down it in patient-derived xenografts (PDX) cells using lentiviral shRNA constructs. The silencing of LAMC2 resulted in decreased self-renewal, invasiveness, tumorigenicity and gemcitabine resistance both in vitro and in vivo. To identify or track the LAMC2 tumor cell population in an intact environment we engineered primary PDAC cells that carry EGFP cassette knocked in the LAMC2 locus through the CRISPR-Cas9 technique. Analysis of LAMC2-EGFP+ cells isolated from tumor demonstrated that these cells express a gene program similar to that of highly metastatic stem cells and that they initiate and propagate both the primary tumor and the metastasis to recipient mice very efficiently compared to their counterpart. In conclusion, we identified a highly metastatic subpopulation of cancer stem cells, characterized by high levels of LAMC2. Strategies aimed at targeting the LAMC2 population may be effective in reducing tumor aggressiveness in combination with conventional therapy.

Citation Format: Donatella Delle Cave, Tea Teresa Iavazzo, Maria Mangini, Gennaro Andolfi, Teresa Pirozzi, Annalisa Di Domenico, Annachiara De Luca, Enza Lonardo. LAMC2: New player in stemness and tumor progression in pancreatic cancer [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2021 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2021;81(22 Suppl):Abstract nr PO-038.

A serine 37 mutation associated with two missense mutations at highly conserved regions of p53 affect pro-apoptotic genes expression in a T-lymphoblastoid drug resistant cell line

The p53 protein accumulates rapidly through post-transcriptional mechanisms following cellular exposure to DNA damaging agents and is also activated as a transcription factor leading to growth arrest or apoptosis. Phosphorylation of p53 occurs after DNA damage thereby modulating its activity and impeding the interaction of p53 with its negative regulator oncogene Mdm2. The serines 15 and 37 present in the amino terminal region of p53 are phosphorylated by the DNA-dependent protein kinase (DNA-PK) in response to DNA damage. In order to verify if specific p53 mutations occur in the multi-drug resistance phenotype, we analysed the p53 gene in two T-lymphoblastoid cell lines, CCRF-CEM and its multi-drug-resistant clone CCRF-CEM VLB100, selected for resistance to vinblastine sulfate and cross-resistant to other cytotoxic drugs. Both cell lines showed two heterozygous mutations in the DNA binding domain at codons 175 and 248. The multi-drug resistant cell line, CCRF-CEM VLB100, showed an additional mutation that involves the serine 37 whose phosphorylation is important to modulate the protein activity in response to DNA damage. The effects of these mutations on p53 transactivation capacity were evaluated. The activity of p53 on pro-apoptotic genes expression in response to DNA damage induced by (-irradiation, was affected in the vinblastine (VLB) resistant cell line but not in CCRF-CEM sensitive cell line resulting in a much reduced apoptotic cell death of the multi-drug resistant cells.

Molecular cloning, expression and site-directed mutagenesis of glutathione S-transferase from Ochrobactrum anthropi

The gene coding for a novel glutathione S-transferase (GST) has been isolated from the bacterium Ochrobactrum anthropi. A PCR fragment of 230 bp was obtained using oligonucleotide primers deduced from N-terminal and 'internal' sequences of the purified enzyme. The gene was obtained by screening of a genomic DNA partial library from O. anthropi constructed in pBluescript with a PCR fragment probe. The gene encodes a protein (OaGST) of 201 amino acids with a calculated molecular mass of 21738 Da. The product of the gene was expressed and characterized; it showed GST activity with substrates 1-chloro-2, 4-dinitrobenzene (CDNB), p-nitrobenzyl chloride and 4-nitroquinoline 1-oxide, and glutathione-dependent peroxidase activity towards cumene hydroperoxide. The overexpressed product of the gene was also confirmed to have in vivo GST activity towards CDNB. The interaction of the recombinant GST with several antibiotics indicated that the enzyme is involved in the binding of rifamycin and tetracycline. The OaGST amino acid sequence showed the greatest identity (45%) with a GST from Pseudomonas sp. strain LB400. A serine residue in the N-terminal region is conserved in almost all known bacterial GSTs, and it appears to be the counterpart of the catalytic serine residue present in Theta-class GSTs. Substitution of the Ser-11 residue resulted in a mutant OaGST protein lacking CDNB-conjugating activity; moreover the mutant enzyme was not able to bind Sepharose-GSH affinity matrices.