Tetracycline regulated protein expression in mammalian cells is a powerful tool to predict the physiological function, cellular localization, and stability of a protein. In addition, to predict metabolic networks affected by the expression of wild-type or mutant forms of proteins, researchers generally produce a single mammalian cell clone that can express the protein of interest under tetracycline control and study the changes occurring in overall proteome before and after expression of a protein of interest. One limitation of tetracycline regulated clonal cell creation, however, is that it sometimes creates clones with changed protein levels even without the expression of the protein of interest due to the nonspecific insertion of the gene encoding the protein of interest into the genome or disruption of a metabolic pathway due to insertional silencing or activation. The aim of this study was to demonstrate the limitation of tetracycline regulated gene expression by creating clonal cell lines expressing the wild-type or the mutant forms of Fat mass and obesity-associated protein. Comparative proteome analysis of the protein extracts by two-dimensional gel electrophoresis coupled to MALDI-TOF/TOF revealed the presence of eight proteins subjected to differential regulation even in the absence of induction. The identified proteins were 14-3-3 protein Epsilon, Vimentin, Heterogeneous nuclear ribonucleoprotein K, Tubulin beta-2C chain, Heat shock protein HSP 90-alpha, Heat shock protein HSP 90-beta, Alpha-enolase, TATA-binding protein-associated factor 2N. An ultimate care should be taken to prevent reporting of deceitful proteins generated from studies utilizing tetracycline regulated gene expression systems.