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Activation of human squamous cell carcinoma ornithine decarboxylase activity by guanosine triphosphate
O Hietala1, L Dzubow, A A Dlugosz
1Wistar Institute of Anatomy and Biology, Philadelphia, Pennsylvania 19104.
Abstract:
Previous studies have demonstrated the presence in mouse epidermal tumors of a structurally and functionally altered ornithine decarboxylase (ODC). In this report, the enzymatic properties of ODC from normal human skin and squamous cell carcinomas are examined. Some tumors contained a more heat stable ODC than the enzyme found in normal skin. GTP stimulated enzyme activity in four of seven tumor extracts tested but had no effect on normal skin ODC. Kinetic analyses indicated that GTP either lowered the apparent Km of tumor ODC for L-ornithine, increased the Vmax, or had both effects, depending on the tumor examined. Gel filtration chromatography of crude tumor extracts indicated the existence of multiple molecular weight forms of ODC, some of which can be activated by GTP and some of which are unaffected by GTP. Some tumors contain both a GTP-activatable and -nonactivatable form of the enzyme. Immunolocalization studies demonstrated the presence within squamous cell carcinomas of cells with a constitutively high level of immunoreactive ODC, a situation never observed in normal skin tissue. These results suggest that some human squamous cell carcinomas contain a functionally altered ODC that may be aberrantly regulated.
Insights
Human skin cancer cells show altered ornithine decarboxylase (ODC) enzyme activity. This key enzyme may be aberrantly regulated in squamous cell carcinomas, offering potential new therapeutic targets.
Area of Science:
- Biochemistry
- Oncology
- Dermatology
Background:
- Previous studies identified altered ornithine decarboxylase (ODC) in mouse skin tumors.
- ODC is a critical enzyme in polyamine synthesis, linked to cell growth and proliferation.
Purpose of the Study:
- To investigate the enzymatic properties of ODC in normal human skin and human squamous cell carcinomas.
- To determine if ODC in tumors exhibits altered heat stability, GTP responsiveness, and molecular forms compared to normal skin ODC.
Main Methods:
- Enzyme assays were performed on ODC extracted from normal human skin and squamous cell carcinoma tissues.
- GTP stimulation assays, kinetic analyses (Km, Vmax), gel filtration chromatography, and immunolocalization were utilized.
Main Results:
- Some tumor ODC exhibited increased heat stability compared to normal skin ODC.
- GTP stimulated ODC activity in 4/7 tumor extracts, altering kinetic parameters (Km, Vmax) variably.
- Gel filtration revealed multiple ODC molecular weight forms in tumors, some GTP-activatable and some not.
- Immunolocalization showed constitutively high ODC levels in tumor cells, unlike normal skin.
Conclusions:
- Human squamous cell carcinomas can contain functionally altered ODC.
- These alterations include changes in heat stability, GTP regulation, and molecular forms.
- Aberrant regulation of ODC in these tumors suggests its potential role in cancer development and progression.