Immortality and growth factor signaling
Reactivation and expression of telomerase is an important hallmark for around 85% of all tumors to maintain telomeres and gain immortality by overcoming molecular senescence. ALT is less commonly used, but show high prevalence in sarcoma and astrocytoma.
In cooperation with clinical partners we focused on the role of TMMs in human glioblastoma multiform (GBM), an aggressive form of astrocytoma brain tumors (Sampl et al, 2012).
Our data support the known high prevalence of ALT in low-grade astrocytoma and better clinical outcome in GBM with ALT. TMM was evaluated by measuring TA and by detection of long telomeres typically seen with ALT. TA positive cells show mean of 5-10 kbp, whereas in ALT cells up to 20 kbp telomere length (TL). Long non–coding telomeric repeat–containing RNA transcripts (TERRA or TelRNA) have been reported as key component of telomeres with inhibitory function on telomerase.
We demonstrated by qPCR that TERRA expression clearly correlates with tumor grade and TMM (Figure 1). TERRA expression correlated to outcome of this patient series indicating that TERRA may be prognostic in astrocytoma.
Next, we set up a recombinant TERRA expression system (Kreilmeier et al, 2016a) to evaluate TERRA effects in vitro (Figure 2). With a commercial partner we used this system to study combinatorial effects in tumor cells. Furthermore, we were able to identify recently the ALT mechanisms in canine tumors, important for comparative research (Kreilmeier et al, 2016b).
In cooperation with partners from Veterinary Universities we performed FGF receptor (FGFR) expression studies on soft tissue sarcoma (STS) in a comparative setting on human and canine species (Schweiger et al, 2015).
We identified FGFR1 as most abundant expressed member of the FGFR family in STS. Alternative splicing of the IgIII loop of FGFRs 1-3 leads to b- and c-variants, involved in epithelial mesenchymal transition important for metastatic features during tumor progression.
We developed STS and colorectal cancer (CRC) tumor cell models with splice reporter systems using fluorescent proteins (Holzmann et al, 2012). Such systems allow in vivo and in vitro real-time observation of splice choices in single cells (Figure 3).
Together with clinical partners, we identified ESRP1 and ESRP2 splicing regulatory proteins as essential for FGFR variant splicing in CRC progression and as potential independent prognostic markers for patient survival (Deloria et al, 2016).