Endocrine Abstracts

JOINT2710

Objective: Recognised by aggressive behaviour, silent corticotroph adenomas (SCA) represent up to 15% of non-functioning pituitary neuroendocrine tumours (PitNETs). Clinical presentation is usually related to tumour volume without hypercortisolism-related symptoms. We have previously shown that gene and protein levels of PDZ and LIM domain 1 (PDLIM1) are significantly upregulated in SCA when compared with normal functioning corticotroph adenomas (FCA) ¹. PDLIM1 plays important roles in cellular homeostasis and cytoskeletal organization, affecting morphological changes and migration. Tumorigenesis-related role is divergent, being a contributor in gastric cancer, glioma, and breast cancer, but a protector in colorectal and hepatocellular carcinoma. We hypothesized that PDLIM1 is involved in the aggressiveness of SCA. We aimed to assess the roles of PDLIM1 in corticotroph adenomas’ aggressiveness and identify the responsible mechanisms.

Methods: Clinical, biochemical and imaging characteristics were obtained from a cohort of 50 patients (17 SCA and 33 FCA). PDLIM1 gene expression was measured by RT-qPCR in tumour tissue. AtT-20 mouse pituitary corticotroph tumour cells were transfected with pCMV6-Entry plasmid containing Pdlim1, and three clones with stable Pdlim1 overexpression were selected by western blotting, expanded and used in CCK-8 cell proliferation and transwell migration assays. Furthermore, quantitative label-free mass spectrometry (MS)–based proteomics analysis was performed on cell lysate of each clone and wild-type (WT) AtT-20.

Results: SCA was larger in size than FCA (max diameter mean 26 vs 7 mm, P<0.005). All of SCA were macroadenoma (n=17), whereas FCA were both macro- and microadenoma (n=11 and 22, respectively). SCA expressed higher PDLIM1 expression as compared to FCA (P<0.01). All selected clones with stable Pdlim1 overexpression showed morphological changes: each contained suspension cell clusters, floating or hanging with adherent groups. Some adherent parts exhibited string-like fibroblastic appearance. The clones showed increased proliferation and migration (P<0.0001) as compared to WT cells. Proteomics analyses showed upregulation of Pdlim1, Igfbp4, Itgb3, Pcsk1n and Stc1 in all clones (P<0.05, for all). Furthermore, two clones showed upregulation of Ctsb, Igfbp5, Mcam, and Plin2 (q<0.05, for all). Ctsb, Igfbp4/5, Itgb3, Mcam and Stc1 are known to be involved in migration, invasion, and proliferation in other tumours. Pathway analyses showed activation of regulation of Insulin-like growth factor transport whereas lipid metabolism by PPARalpha, cholesterol biosynthesis, and gene expression activation by SREBP were inhibited.

Conclusion: PDLIM1 is upregulated in SCA and seems to contribute to proliferation and migration of corticotroph tumour cells.

References: 1. https://dx.doi.org/10.3390/cancers12102980.