Phorbol myristate acetate and Bryostatin 1 rescue IFN-gamma inducibility of MHC class II molecules in LS1034 colorectal carcinoma cell line

Our plain-English summary of Phorbol myristate acetate and Bryostatin 1 rescue IFN-gamma inducibility of MHC class II molecules in LS1034 colorectal carcinoma cell line, by Y. Kudinov, C.L. Wiseman, A.I. Kharazi (Cancer Cell International, 2003).

The study

• Authors: Y. Kudinov, C.L. Wiseman, A.I. Kharazi
• Journal: Cancer Cell International
• Published: 2003;3:4
• Cited by: 11 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: The expression of major histocompatibility complex class II (MHCII) antigens in both mouse and human tumors is rare, and these antigens are not easily inducible by IFN-gamma (IFNg). Since MHCII may play an important role in the development of host antitumor immune response, we explored the possibility of restoring MHCII inducibility in several IFNg-resistant tumor cell lines using protein kinase C (PKC) agonists phorbol myristate acetate (PMA) or Bryostatin.

Results: Tumor cells were co-cultured with various concentrations of PMA and IFNg for 48 hr. The expression of MHCII antigens and receptors IFNgR1 and IFNgR2 was determined by flow cytometry. We showed that the presence of as little as 0.1 ng/ml of PMA in tissue culture restored the ability of weakly inducible LS1034 colon carcinoma cells to express MHCII in response to IFNg (100 - 10,000 IU/ml) in a dose-dependent manner. Likewise, Bryostatin 1, as low as 10 ng/ml produced a 5-6 fold upregulation of MHCII. The effect of PMA was not observed in two other poorly responding cell lines, MSTO-211H mesothelioma and HepG2 hepatocellular carcinoma, and was abrogated by relatively high concentrations of PKC inhibitors staurosporine (100 nM) and GF 109203X (1,000 nM). Both surface and intracellular staining of all cell lines with antibodies against IFNgR1 and IFNgR2 failed to detect any increase in IFNg receptor expression following incubation with PMA.

Conclusion: In this study we showed that IFNg-inducibility of MHCII antigens in weakly inducible LS1034 colorectal carcinoma cell line can be rescued by concomitant incubation with PKC agonists. Bryostatin 1 may be considered for further investigation of IFNg-dependent MHCII induction in resistant tumors in vivo.

In plain English

This laboratory study used human tumor cell lines grown in dishes; it involved no people or animals and no asbestos. The authors tested whether two activators of the enzyme protein kinase C, PMA and the clinically tested drug Bryostatin 1, helped tumor cells display immune molecules called MHC class II after interferon-gamma treatment. The lines were colon cancer LS1034 and SW480, mesothelioma MSTO-211H, and liver cancer HepG2. With interferon-gamma alone, LS1034 showed only a 1.4- to 1.6-fold increase and the mesothelioma line a weak response. PMA did not help the mesothelioma or liver lines. In LS1034, PMA plus interferon-gamma substantially increased MHC class II. Differences between PMA concentrations were not statistically significant overall (P = 0.14) but were significant when ethanol was also present (P = 0.043). Bryostatin 1 at 10 ng/ml plus interferon-gamma produced a 5- to 6-fold increase in LS1034. The authors concluded that adding protein kinase C activators alongside interferon-gamma can rescue the weak LS1034 response in culture. They noted that the clinical implications are difficult to judge.

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 (in vitro) experiment on human tumor cell lines
• Who was studied: Four human tumor cell lines bought from the American Type Culture Collection: LS1034 colorectal carcinoma, SW480 colorectal adenocarcinoma (a strongly responding comparison line), MSTO-211H biphasic mesothelioma, and HepG2 hepatocellular carcinoma. The work was done at the Immunotherapy Laboratory, St. Vincent Medical Center, Los Angeles.
• Exposure: No asbestos or fiber exposure was studied. Cells were treated for 48 hours with interferon-gamma (100 to 10,000 IU/ml) combined with PMA, which the article calls a potent protein kinase C activator, or with Bryostatin 1, which it calls a clinically tested drug. Some PMA cultures also contained ethanol (172 mM). Separate tests used the kinase inhibitors staurosporine and GF 109203X.
• Main results:
  • With interferon-gamma alone, LS1034 cells showed only a weak (1.4- to 1.6-fold) increase in MHC class II, compared with a 10-fold increase in SW480 cells.
  • The MSTO-211H mesothelioma cell line showed only a weak response to interferon-gamma alone.
  • PMA did not improve the interferon-gamma response in the MSTO-211H mesothelioma or HepG2 liver cancer cell lines.
  • In LS1034 cells, combined treatment with PMA and interferon-gamma substantially increased MHC class II expression.
  • In a two-factor analysis that compared different nonzero PMA concentrations in LS1034 cells, the overall effect of PMA concentration was not statistically significant (P = 0.14).
  • In the same comparison of PMA concentrations, restricted to LS1034 cultures that also contained 172 mM ethanol, the effect of PMA was statistically significant (P = 0.043).
  • Ethanol significantly improved MHC class II induction in LS1034 cells when PMA was present. The authors report that ethanol alone was inactive.
  • PMA with ethanol did not change the levels of interferon-gamma receptors on LS1034 cells.
  • In LS1034 cells, the PMA-enhanced response was blocked by 100 nM staurosporine or by 1 µM GF 109203X.
  • In LS1034 cells, Bryostatin 1 at 10 ng/ml, added to medium containing 100 to 1,000 IU/ml interferon-gamma, produced a 5- to 6-fold increase in MHC class II. The effect leveled off at 10 ng/ml.
  • At the higher interferon-gamma concentration (1,000 IU/ml), PMA was much more effective than Bryostatin 1 in LS1034 cells.
  • All four cell lines expressed the retinoblastoma (Rb) protein.
• The authors' conclusion: The authors concluded that the weak interferon-gamma response of MHC class II in LS1034 colorectal carcinoma cells can be rescued by incubating the cells with protein kinase C activators at the same time. They also concluded that Bryostatin 1 may be considered for further study in resistant tumors in living systems.
• Limitations the authors state:
  • The size of the LS1034 response varied greatly from one experiment to the next.
  • It is not known whether the effect is unique to the LS1034 cell line.
  • The clinical implications of these laboratory findings are difficult to evaluate.

Topics

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

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