Noncanonical GLI1 signaling promotes stemness features and in vivo growth in lung adenocarcinoma

Abstract

Aberrant Hedgehog/GLI signaling has been implicated in a diverse spectrum of human cancers, but its role in lung adenocarcinoma (LAC) is still under debate. We show that the downstream effector of the Hedgehog pathway, GLI1, is expressed in 76% of LACs, but in roughly half of these tumors, the canonical pathway activator, Smoothened, is expressed at low levels, possibly owing to epigenetic silencing. In LAC cells including the cancer stem cell compartment, we show that GLI1 is activated noncanonically by MAPK/ERK signaling. Different mechanisms can trigger the MAPK/ERK/GLI1 cascade including KRAS mutation and stimulation of NRP2 by VEGF produced by the cancer cells themselves in an autocrine loop or by stromal cells as paracrine cross talk. Suppression of GLI1, by silencing or drug-mediated, inhibits LAC cells proliferation, attenuates their stemness and increases their susceptibility to apoptosis in vitro and in vivo. These findings provide insight into the growth of LACs and point to GLI1 as a downstream effector for oncogenic pathways. Thus, strategies involving direct inhibition of GLI1 may be useful in the treatment of LACs.

Targeting cancer stem cell pathways for cancer therapy

“…For example, Hh signaling promotes the maintenance, proliferation, self-renewal, and tumorigenicity of lung adenocarcinoma stem cells. 240 In CD133 + glioma stem cells, SMO, GLI, and PTCH promote cell proliferation, self-renewal, migration, and invasion. The expression of Gli1, PTCH1, and PTCH2 is regulated by histone deacetylase 6.…”

Stromal Hedgehog pathway activation by IHH suppresses lung adenocarcinoma growth and metastasis by limiting reactive oxygen species

“…We evaluated the impact of SHH expression on lung adenocarcinoma (LAD) patients as SHH is the primary Hh ligand critical for lung development (51–54), adult lung airway homeostasis (55, 56), and reported in lung cancers (42, 43, 46, 50, 57). We assessed the impact of high SHH mRNA expression in LAD patients in the Kaplan-Meier Plotter (KM-Plotter; (58, 59)) database that aggregates Affymetrix microarray mRNA expression with clinical annotation.…”

“…A surprising result of our studies was the central role of IHH, instead of SHH, to suppress tumor growth. SHH is the dominant ligand that regulates lung development (51–54, 91), adult lung airway homeostasis (55, 56, 92), and lung cancers (42, 43, 46, 50, 57). IHH is expressed in the adult colon (93) and prostate (90) and restrains the growth of colon (40, 94) and prostate (41) cancers.…”

“…GLI1 activation drove LSCC growth and treatment with combinatorial PI3K and GLI1 antagonists leads to tumor regression in vivo (49). In LAD tumor-spheres and cell lines, paracrine SHH from LAD epithelia activated the pathway in stroma to express VEGF that in turn, bound to NRP2 receptor to activate the MAPK pathway and express GLI1 in a non-canonical manner (50). Given these varied results of the pathway’s role and modes of action in lung cancers and other solid tumors, we tested the role of paracrine Hh pathway activation in LAD tumorigenesis and growth in autochthonous mutant Kras G12D/+ ;Trp53 fl/fl mouse models of LAD.…”

Stromal Hedgehog pathway activation by IHH suppresses lung adenocarcinoma growth and metastasis by limiting reactive oxygen species

“…GLI1 activation drove LSCC growth and treatment with combinatorial PI3K and GLI1 antagonists induced tumor regression in vivo [31]. In LAD tumor-spheres and cell lines, paracrine SHH from LAD epithelia activated the pathway in stroma to express VEGF that in turn, bound to NRP2 receptor to activate the MAPK pathway and express GLI1 in a non-canonical manner [32]. Given these varied results of the pathway's role and modes of action in lung cancers and other solid tumors, we tested the role of paracrine Hh pathway activation in LAD tumorigenesis and growth in autochthonous mutant Kras G12D/+ ;Trp53 fl/fl mouse model of LAD.…”