Understanding pathway signaling enables the precise targeting of key mechanisms of action, facilitates biomarker identification, and helps predict resistance to therapies, crucial for developing effective therapeutic strategies.
Cellular pathways altered during the early stages of tumorigenesis
In the early stages of tumorigenesis, cells begin to acquire mutations and epigenetic changes that disrupt normal regulatory mechanisms.
Among the DNA lesions, the most dangerous double-strand breaks (DSBs) can result from endogenous sources such as reactive oxygen species (ROS) produced during chronic inflammation, as well as exogenous agents like ultraviolet (UV) radiation and ionizing radiation. Aging also contributes to DNA damage accumulation, increasing cancer risk.
Cells rely on the DNA damage response (DDR) to detect and respond to DNA breakage, regulate cell cycle checkpoints, DNA repair, and apoptosis. Mutations in the DDR genes promote genomic instability and mutations.
Disruption of cell cycle regulation control through mutations in response to DNA damage mediators, like TP53, and CDKN2A, or proliferative signals, such as E2F, RAS, RAF, and G1/S cyclin-dependent kinases (CDKs) allows unchecked DNA synthesis and prevent cell cycle arrest, promoting malignant growth.
Impaired apoptosis is another hallmark of tumorigenesis, exemplified by BCL2 in follicular lymphoma. Epigenetic silencing of tumor suppressors and telomere dysfunction add to instability, while microenvironmental factors like inflammation amplify DNA damage.
Together, these events establish genomic instability, uncontrolled proliferation, and apoptosis resistance: hallmarks that set the stage for malignant growth.
Specific mutations in oncogenes or tumor suppressor genes influence the activation of downstream signaling pathways
Mutations that drive tumorigenesis typically affect two main classes of genes: oncogenes and tumor suppressor genes. These alterations disrupt the balance of growth and death signals.
KRAS, the most commonly mutated RAS family member, acquires gain-of-function mutations that lock the protein in an active state, leading to constant activation of the RAS/MAPK pathway, which drives continuous cell proliferation, survival, and differentiation, regardless of extracellular growth signals.
Similarly, phosphorylation of AKT by PIP3 activates downstream pathways regulating survival, growth, proliferation. PTEN, a lipid phosphatase, normally counteracts these signals by converting PIP3 back into PIP2, thereby limiting PIP3’s activation of AKT. Loss or inactivation of PTEN through deletion or a loss-of-function mutation, this negative mechanism is removed, leading to unchecked PI3K/AKT signaling. The resulting hyperactivation promotes enhanced cellular survival, growth, and metabolic activity.
TP53 encodes the p53 protein, a transcription factor that plays a central role in responding to cellular stress and DNA damage. The p53 protein controls the biological response based on cellular stress signal inputs such as stress oncogene activation, DNA damage, and replication stress (i.e.: impaired or stalled DNA replication). In response to these signals, p53 undergoes post-translational modifications, promoting the transcription of genes that induce cell cycle arrest, initiate DNA repair, or trigger apoptosis.
Loss-of-function mutations in TP53 compromise the cell’s ability to respond to stress signals, leaving cells with damaged DNA to divide, contributing to the accumulation of additional oncogenic mutations.
These pathways are highly interconnected: loss of p53 accelerates acquisition of KRAS or PI3K mutations, while simultaneous activation of MAPK and PI3K/AKT strongly promotes tumor progression. Many of these genes are targets of current or emerging precision cancer therapies.
Crosstalk among different signaling pathways contribute to cancer progression
Interactions between signaling pathways play a central role in cancer progression by deregulating key cellular processes.
Two major oncogenic cascades, the PI3K-Akt and Ras-ERK pathways, interact and converge to drive uncontrolled proliferation, survival, metabolic reprogramming, invasion, and angiogenesis.
When dysregulated by mutations in PTEN or p53, they drive cancer progression. These pathways stabilize Myc and influence metabolic and transcriptional programs.
Crosstalk occurs via shared effectors such as mTORC1 and transcription factors like NF-kB and AP1. These pathways influence other systems including Wnt, Notch, Hedgehog, and Hippo, which regulate differentiation, migration, and stemness.
The resulting crosstalk creates a signaling web that fosters cancer proliferation, survival, immune evasion, and stemness.
At the same time, these interconnections create new therapeutic opportunities, and scRNA-seq is the technology that can capture and decode the full signalling “conversation.”
DNA Damage, Oncogenic Signaling, and Tumor Evolution at High Resolution
ScRNA-seq is uniquely positioned to dissect the early molecular events of tumorigenesis and the evolution of oncogenic signaling.
As these events happened simultaneously in hundreds of thousands of diverse cells, single cell transcription analysis captures the expression of each cell and reveals their transitional state.
For instance, it can reveal how a single population of cancer cells diversifies into three distinct transcriptomic phenotypes in response to DNA damage, each characterized by unique, group-specific gene expression signatures. This is crucial in identifying how disrupted DNA damage response networks contribute to unchecked cell cycle progression and impaired apoptosis.
Dissecting key pathways at the single cell level can reveal new targets to improve therapeutic response: in medulloblastoma (MB) scRNA-seq with combinatorial barcoding was used to investigate OLIG2 expression across MB subgroups to assess the therapeutic potential of OLIG2 inhibition using a novel small molecule, CT-179. OLIG2 is a promising target as it is a transcription factor driving cells from quiescence to proliferation, thus promoting the tumor progression and recurrence. The use of the drug CT-179 reduced tumor growth, particularly in SHH-MB, an aggressive type of medulloblastoma.
Ask a Single Cell
Translate the Conversation
In cells, signaling pathways coordinate growth, survival, differentiation, and death through tightly regulated checkpoints. When these pathways malfunction through oncogenic mutations, loss of tumor suppressors, or aberrant cross-talk, the regulatory balance collapses. Growth-promoting signals remain active, cell cycle checkpoints are bypassed, and stress or damage cues are ignored. The result is uncontrolled proliferation, enhanced survival, metabolic reprogramming, and ultimately tumor progression.
Cause of signaling pathways alterations
- How does chronic inflammation amplify DNA damage?
- What pathways are influenced by DDR? And what are the consequences of mutations within these pathways?
Effect of hub genes mutations in oncogenesis
- Some genes encode hub proteins at the crossroads of key pathways. How do mutations in these genes alter signaling, and what are the consequences for the cell?
- How do mutations in hub genes reshape single-cell transcriptional states and signaling heterogeneity within tumors?
- What therapeutic benefits could be achieved by targeting hub genes at the intersection of key signaling pathways?
Tumor cells evolution
- The same cancer-causing mutation can influence cells in the same tissue differently. Which subpopulations of cells follow different lineage trajectories after the mutation?
- Are lineage-specific transcription factors expressed differently across subpopulations?
- Does disrupting specific abnormal interactions normalize differentiation?
TLDR: Tumor initiation and progression are shaped by sustained rewiring of signaling pathways that control growth, survival, and stress responses. Alterations in key regulatory nodes propagate through interconnected networks, reshaping downstream gene expression programs that support malignancy. These effects vary across cells, creating hidden diversity in pathway activity and therapeutic sensitivity. Single cell RNA sequencing resolves this functional complexity, linking upstream pathway disruptions to downstream transcriptional consequences and revealing vulnerabilities that are masked in aggregate measurements.
