Troponin T Type 1, Slow Skeletal (TNNT1)?is a regulatory complex located on the thin filament of the sarcomere. TNNT1 plays a crucial role in the regulation of muscle contraction, specifically in slow-twitch skeletal muscle fibers. As a key component of the troponin complex, which also includes troponin I and troponin C, TNNT1 interacts with actin, tropomyosin, and calcium ions to modulate the contraction-relaxation cycle of muscle tissue. Previous research has indicated that TNNT1 can promote cell proliferation.To test the effect of TNNT1 on cell proliferation, MCF-7 cells were seeded into triplicate wells of 96-well plates and allowed to attach, replaced with various concentrations of recombinant humanTNNT1. After incubated for 72h, cells were observed by inverted microscope and cell proliferation was measured by Cell Counting Kit-8 (CCK-8). Briefly, 10 μl of CCK-8 solution was added to each well of the plate, then the absorbance at 450 nm was measured using a microplate reader after incubating the plate for 1-4 hours at 37 ℃. Cell viability was assessed by CCK-8 assay after incubation with recombinant human TNNT1 for 72h. The result was shown in Figure 1. It was obvious that TNNT1 significantly increased cell viability of MCF-7 cells. The ED50 of recombinant humanTNNT1 is 1.034 μg/ml.