An immature, dedifferentiated, and lineage-deconstrained cone precursor origin of N-Myc-initiated retinoblastoma

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 119; no. 28; p. e2200721119
• Main Authors: Singh, Hardeep P, Shayler, Dominic W H, Fernandez, G Esteban, Thornton, Matthew E, Craft, Cheryl Mae, Grubbs, Brendan H, Cobrinik, David
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 12-07-2022
• Subjects: Arrestin; Biological Sciences; Cancer; Carcinogenesis - genetics; Cell Cycle; Cell lineage; Cell proliferation; Cell signaling; Cyclin D2; Deregulation; Humans; INK4a protein; Invasiveness; Markers; Mutation; Myc protein; N-Myc protein; N-Myc Proto-Oncogene Protein - genetics; N-Myc Proto-Oncogene Protein - metabolism; p16 Protein; Phosphorylation; Precursors; Progenitor cells; Retina; Retinal cells; Retinal Cone Photoreceptor Cells - metabolism; Retinal Cone Photoreceptor Cells - pathology; Retinal Neoplasms - metabolism; Retinal Neoplasms - pathology; Retinoblastoma; Retinoblastoma - metabolism; Retinoblastoma - pathology; Signaling; Sox9 protein; Stem cells; Tumorigenesis; Tumors; Xenografts; Xenotransplantation; cone precursor; dedifferentiation; MYCN; retinoblastoma; cancer cell of origin
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.2200721119

Most retinoblastomas develop from maturing cone precursors in response to biallelic
loss and are dependent on cone maturation-related signaling. Additionally, ∼2% lack
mutations but have
amplification (
), N-Myc protein overexpression, and more rapid and invasive growth, yet the
retinoblastoma cell of origin and basis for its responses to deregulated N-Myc are unknown. Here, using explanted cultured retinae, we show that ectopic N-Myc induces cell cycle entry in cells expressing markers of several retinal types yet induces continuous proliferation and tumorigenesis only in cone precursors. Unlike the response to
loss, both immature cone arrestin-negative (ARR3
) and maturing ARR3
cone precursors proliferate, and maturing cone precursors rapidly dedifferentiate, losing ARR3 as well as L/M-opsin expression. N-Myc-overexpressing retinal cells also lose cell lineage constraints, occasionally coexpressing the cone-specific RXRγ with the rod-specific NRL or amacrine-specific AP2α and widely coexpressing RXRγ with the progenitor and Müller cell-specific SOX9 and retinal ganglion cell-specific BRN3 and GAP43. Mechanistically, N-Myc induced Cyclin D2 and CDK4 overexpression, pRB phosphorylation, and SOX9-dependent proliferation without a retinoma-like stage that characterizes pRB-deficient retinoblastoma, despite continuous p16
expression. Orthotopic xenografts of N-Myc-overexpressing retinal cells formed tumors with retinal cell marker expression similar to those in
-transduced retinae and
retinoblastomas in patients. These findings demonstrate the
retinoblastoma origin from immature and lineage-deconstrained cone precursors, reveal their opportunistic use of an undifferentiated retinal progenitor cell feature, and illustrate that different cancer-initiating mutations cooperate with distinct developmental stage-specific cell signaling circuitries to drive retinoblastoma tumorigenesis.