The cellular localization of autotaxin impacts on its biological functions in human thyroid carcinoma cells

Area of Science:

• Molecular Biology
• Cancer Research
• Biochemistry

Background:

• Autotaxin (ATX/NPP2) is an enzyme with nucleotide pyrophosphatase/phosphodiesterase and lysophospholipase D activity.
• ATX is unique among mammalian ecto-nucleotide pyrophosphatase/phosphodiesterases (E-NPP) due to its secreted nature, unlike membrane-bound NPP1 and -3.
• Elevated ATX gene activity is observed in undifferentiated anaplastic thyroid carcinoma (UTC) compared to follicular (FTC), papillary (PTC), or goiter tissues, and ATX enhances thyroid tumor cell motility.

Purpose of the Study:

• To bio-engineer stable transfectants of the human thyroid carcinoma cell line FTC-238 expressing either secreted ATX (sATX) or membrane-anchored ATX (mATX).
• To identify biological functions of ATX dependent on its secreted form and understand cellular responses to high local ATX concentrations.
• To investigate the role of IL-1beta in regulating ATX expression and motility, and to identify novel ATX target genes in thyroid carcinoma.

Main Methods:

• Creation of stable FTC-238 transfectants expressing sATX or mATX.
• Assessment of cell motility and anchorage-independent colony formation (soft agar assay).
• Analysis of IL-1beta's effect on ATX expression and motility.
• Identification and quantification of cancer-testis antigen BAGE transcript levels.

Main Results:

• Increased cell motility was exclusively observed in FTC-238 sATX transfectants; mATX appeared to impair motility.
• Both sATX and mATX increased anchorage-independent colony formation, but FTC-238 sATX clones showed significantly larger and more numerous colonies.
• IL-1beta suppressed ATX expression and motility, with the strongest suppressive effect on FTC-238 sATX clones.
• The cancer-testis antigen BAGE was identified as a novel ATX target gene, with 6-fold higher transcript levels in FTC-238 mATX versus sATX clones.
• Increased BAGE transcript levels were also found in UTC tissues compared to FTC, PTC, or goiter tissues.

Conclusions:

• Enhanced tumor cell motility and tumorigenic capacity in thyroid carcinoma are critically dependent on secreted ATX (sATX).
• The cancer-testis antigen BAGE is a novel target gene of ATX, irrespective of its compartmentalization (secreted or membrane-anchored).
• BAGE represents a potential new tissue marker for undifferentiated thyroid carcinoma (UTC) tissues, which exhibit high ATX levels.