Fig. 4

Protein encoding circE7 is essential for CaSki cell growth. a CaSki cells were lentivirally transduced with doxycycline (dox)-inducible hairpins specific for the circE7 backsplice junction (circE7 sh1/2). RT-qPCR for levels of circE7 revealed that circE7 sh1/2 resulted in significant decreases of circE7 levels. (n = 3 independent experiments, run in duplicate). b Northern blot of RNase R treated total RNA (30 μg) from CaSki cells with or without circE7 sh1/2 induction (2 days). Band density (bottom number) was quantitated and normalized to the uninduced control. c Western blots for E7 and E6 after circE7 sh1/2 induction (3 days). Western blots representative of 3 independent experiments. GAPDH, loading control. d A total of 6.0 × 10⁴ CaSki cells were seeded in triplicate in six-well plates at day 0 and absolute cell number quantitated daily after day 2. CircE7 sh1/2 induction resulted in significantly slower growth of CaSki cells after day 4. Similar results were obtained in 3 independent experiments. e CaSki cells with or without circE7 sh1/2 induction (1 day) were plated in chamber slides and labeled with BrdU (10 μM for 1.5 h). Cells were stained with αBrdU and DAPI and scored as % of DAPI + cells. f 1.0 × 10⁴ CaSki circE7 sh1/2 cells with or without induction (1 day) were seeded in triplicate in soft agar with or without dox (14 days). Average colonies per 35 mm. n = 4 independent transfections. g CaSki were doubly transduced with a shRNA resistant WT circE7 (circResist_WT) and circE7 sh1/2. MTT assay of circResist_WT cells with and without Dox induction. MTT values normalized to the uninduced (-Dox) condition. h CaSki were doubly transduced with a shRNA resistant circE7 with no start codons (circResist_noATG) and circE7 sh1/2. MTT assay of circResist_noATG cells with and without Dox induction. MTT values normalized to the uninduced (-Dox) condition. Data are shown as mean ± s.d. P values (indicated above relevant comparisons) were calculated with two-tailed t test (d, g, h) and one-way analysis of variance (ANOVA) with Holm–Sidak tests (a, e, f). Source data for b, c  provided in Source Data file