Complex sentence: In 1906, the bank acquired Industrial Credit Bank (Τράπεζα Επαγγελματικής Πίστεως; est.1873 in Athens) whose Istanbul branch (opened in 1905) was transferred to Bank of Athens ownership.
Split into simpler sentences: In 1906, the bank acquired the Industrial Credit Bank (Τράπεζα Επαγγελματικής Πίστεως) which had been established in 1873 in Athens. The Industrial Credit Bank's Istanbul branch, which had opened in 1905, was transferred to Bank of Athens ownership.