Comparison of Akt/mammalian target of rapamycin/4E-binding protein 1 pathway signal activation in round stromal and surface cells in patients with sclerosing pneumocytoma

Sclerosing pneumocytoma (SP) is a rare benign epithelial tumor of the lung, and approximately 40 % of patients with SP present with AKT1 E17K mutation. SP cells comprise proliferated surface and round stromal cells. To elucidate the role of signal transductions and to identify the difference between surface and stromal cells, the current study aimed to investigate the activation of the Akt/mammalian target of rapamycin (mTOR)/4E-binding protein 1 signaling pathway in SP. METHODS: The molecular and pathological characteristics of SP in 12 patients were analyzed. AKT1 gene analysis revealed AKT1 E17K mutation in four cases. Immunohistochemical analysis revealed that tumor cells were cytoplasmic positive for pAkt, pmTOR, p4EBP1, and pS6RP. The surface cells had a significantly higher expression of pmTOR (p = 0.002) and a significantly lower expression of p4EBP1 (p = 0.017) than stromal cells. SP without AKT1 E17K mutation had a higher positive correlation with pacts, p4EBP1, pmTOR, and pS6RP expression than SP with AKT1 E17K mutation. These findings may be attributed to the aberrant activation of the Akt/mTOR pathway due to AKT1 E17K mutations. Hence, both surface and round stromal cells have tumorigenic characteristics, and differences in these characteristics may contribute to variations in tumor growth and the morphology and angiogenesis of SP.

Downregulation of RRM2 Attenuates Retroperitoneal Liposarcoma Progression via the Akt/mTOR/4EBP1 Pathway: Clinical, Biological, and Therapeutic Significance

Background

Retroperitoneal liposarcoma (RLPS) is a rare tumor with high recurrence rate. Ribonucleotide reductase small subunit M2 (RRM2) protein is essential for DNA synthesis and replication. Our previous study has demonstrated that RRM2 downregulation inhibited the proliferation of RLPS cells, but further association between RRM2 and RLPS and relevant mechanisms remains to be explored.

Methods

RRM2 expression was evaluated in RLPS tumor tissues and cell lines by using real-time PCR and immunohistochemical analysis. The effect of RRM2 downregulation on cell proliferation, apoptosis, cell cycle, cell migration and invasion was tested by lentivirus. The effect of RRM2 inhibition on tumor growth in vivo was assessed by using patient-derived tumor xenograft (PDX) of RLPS and RRM2 inhibitor. The underlying mechanisms of RRM2 in RLPS were explored by protein microarray and Western blotting.

Results

The results showed that RRM2 mRNA expression was higher in RLPS tissues than in normal fatty tissues (P<0.001). RRM2 expression was higher in the dedifferentiated, myxoid/round cell, and pleomorphic subtypes (P=0.027), and it was also higher in the high-grade RLPS tissues compared to that in the low-grade RLPS tissues (P=0.004). There was no correlation between RRM2 expression and overall survival (OS) or disease-free survival (DFS) in this group of RLPS patients (P>0.05). RRM2 downregulation inhibited cell proliferation, promoted cell apoptosis, facilitated cell cycle from G1 phase to S phase and inhibited cell migration and invasion. Inhibition of RRM2 suppressed tumor growth in NOD/SCID mice. Protein microarray and Western blot verification showed that activity of Akt/mammalian target of rapamycin/eukaryotic translation initiation factor 4E binding protein 1 (Akt/mTOR/4EBP1) pathway was downregulated along with RRM2 downregulation.

Conclusion

RRM2 was overexpressed in RLPS tissues, and downregulation of RRM2 could inhibit RLPS progression. In addition, suppression of RRM2 is expected to be a promising treatment for RLPS patients.