The role of TGFBI in mesothelioma and breast cancer: association with tumor suppression

Our plain-English summary of The role of TGFBI in mesothelioma and breast cancer: association with tumor suppression, by B. Li, G. Wen, Y. Zhao, et al (BMC Cancer, 2012).

The study

• Authors: B. Li, G. Wen, Y. Zhao, J. Tong, T.K. Hei
• Journal: BMC Cancer
• Published: 2012;12:239
• Cited by: 46 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Transforming growth factor β induced (TGFBI) product, an extracellular matrix (ECM) protein, has been implicated as a putative tumor suppressor in recent studies. Our previous findings revealed that expression of TGFBI gene is down-regulated in a variety of cancer cell lines and clinical tissue samples. In this study, ectopic expression of TGFBI was used to ascertain its role as a tumor suppressor and to determine the underlying mechanism of mesothelioma and breast cancer.

Methods: Cells were stably transfected with pRc/CMV2-TGFBI and pRc/CMV2-empty vector with Lipofectamine Plus. Ectopic expression of TGFBI was quantified by using quantitative PCR and Western-blotting. Characterization of cell viability was assessed using growth curve, clonogenic survival and soft agar growth. The potential of tumor formation was evaluated by an in vivo mouse model. Cell cycle was analyzed via flow cytometry. Expressions of p21, p53, p16 and p14 were examined using Western-blotting. Senescent cells were sorted by using a Senescence β-Galactosidase Staining Kit. Telomerase activity was measured using quantitative telomerase detection kit.

Results: In this study, an ectopic expression of TGFBI in two types of cancer cell lines, a mesothelioma cell line NCI-H28 and a breast cancer cell line MDA-MB-231 was found to have reduced the cellular growth, plating efficiency, and anchorage-independent growth. The tumorigenicity of these cancer cell lines as determined by subcutaneous inoculation in nude mice was similarly suppressed by TGFBI expression. Likewise, TGFBI expression reduced the proportion of S-phase while increased the proportion of G1 phase in these cells. The redistribution of cell cycle phase after re-expression of TGFBI was correspondent with transiently elevated expression of p21 and p53. The activities of senescence-associated β-galactosidase and telomerase were enhanced in TGFBI-transfected cells.

Conclusion: Collectively, these results imply that TGFBI plays a suppressive role in the development of mesothelioma and breast cancer cells, possibly through inhibitions of cell proliferation, delaying of G1-S phase transition, and induction of senescence.

In plain English

This laboratory study used cancer cells grown in dishes and injected into mice. It did not study people or asbestos exposure. The authors added the TGFBI gene to two human cancer cell lines, NCI-H28 (malignant pleural mesothelioma) and MDA-MB-231 (breast cancer), and compared them with control cells. Cells carrying TGFBI grew more slowly. Relative plating efficiency measures colony formation compared with the original (parental) cells. It fell from 98.00% to 29.71% for mesothelioma cells and from 98.8% to 73.28% for breast cancer cells. Colony growth in soft agar dropped by 48.54% and 90.89%, respectively. In nude mice, breast cancer cells with TGFBI formed nodules at 12 of 24 injection sites. Parental and empty-vector control cells combined formed nodules at 24 of 24, and the TGFBI tumors were smaller. Mesothelioma cells did not form growing tumors in mice, with or without TGFBI. Cells with TGFBI were slower to enter the cell-cycle stage where DNA is copied. They had raised p21 and p53 protein levels 12 to 24 hours after being stimulated to divide, and showed a cellular aging marker. The authors concluded that TGFBI may act as a tumor suppressor in these cells.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory experiment: human cancer cell lines given the TGFBI gene (or an empty control vector), tested in cell culture and by injection into nude mice
• Who was studied: Two human cancer cell lines from the American Type Culture Collection: malignant pleural mesothelioma line NCI-H28 and breast tumor line MDA-MB-231. Male Nu/Nu (nude) mice were also used, each injected with 5 million cells in both flanks. The number of mice is not stated.
• Exposure: No asbestos or fiber exposure was studied. The experimental factor was artificially introduced (ectopic) expression of the TGFBI gene, compared with empty-vector control cells and parental cells. Asbestos is mentioned only in the background discussion.
• Main results:
  • Population doubling time was 4.38 times longer in the TGFBI mesothelioma cells and 1.16 times longer in the TGFBI breast cancer cells.
  • Plating efficiency was calculated relative to colony numbers of the parental cells. For mesothelioma cells it dropped from 98.00% to 29.71% with TGFBI.
  • Relative plating efficiency (relative to parental cells) of the breast cancer cells dropped from 98.8% to 73.28% with TGFBI.
  • Anchorage-independent (soft agar) growth fell by 48.54% in the TGFBI mesothelioma cells and by 90.89% in the TGFBI breast cancer cells, relative to control cells.
  • In nude mice, TGFBI breast cancer cells produced palpable nodules at 12 of 24 injection sites, which the text calls 50%. Parental cells formed nodules at 12 of 12 sites and empty-vector cells at 12 of 12, pooled as 24 of 24. Mean tumor volume was 251.85 plus or minus 36.16 cubic millimeters with TGFBI, compared with 448.36 plus or minus 107.56 for the pooled controls (P less than 0.01). Tumors appeared about 2 weeks later in the TGFBI group.
  • Mesothelioma cells, both with TGFBI and with the empty control vector, did not produce progressively growing tumors in nude mice. Tumor suppression in mice was therefore tested only with breast cancer cells.
  • Breast tumors from TGFBI cells had significantly fewer cells positive for ki67, a marker of cell division, than tumors from control cells.
  • After serum stimulation, control cells began entering S phase (DNA copying) as early as 4 hours. TGFBI cells did not begin before 20 hours.
  • After serum stimulation, TGFBI cells (T2807 and T23113) showed raised p21 and p53 protein levels at 12 hours and up to 24 hours.
  • Most TGFBI cells stained strongly for senescence-associated beta-galactosidase, a marker of cellular aging. Control cells did not.
  • Telomerase activity was significantly higher in TGFBI mesothelioma cells than in controls (P less than 0.01). In breast cancer cells, neither telomerase activity nor p16 and p14 levels changed. p16 and p14 were also unaffected in mesothelioma cells.
• The authors' conclusion: The authors concluded that TGFBI inhibited cell proliferation and transformation by delaying the G1 to S phase transition and inducing cellular senescence in mesothelioma and breast cancer cells. They described TGFBI as possibly a negative regulator and potential tumor suppressor in these cancers.
• Limitations the authors state:
  • Mesothelioma cells did not form tumors in nude mice. The authors were unsure why, suggested residual immunity in nude mice, and proposed using SCID mice instead.
  • The study did not examine genetic instability.
  • The p16 gene is deleted in NCI-H28 mesothelioma cells. The authors said this made it hard to judge any link between TGFBI and p16.
  • The authors noted other research suggesting TGFBI can promote metastasis in colon and ovarian cancer cell lines and is over-expressed in some other cancers. They suggested it may act differently depending on tissue type.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Mesothelioma.

Medical terms in this study, explained in our Lexicon: Mesothelioma.

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